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THE 

PRINCIPLES   OF    PHYSIOLOGY 

BY 

JOHN    GRAY    McKENDRICK 


LONDON 
WILLIAMS   &   NORGATE 

HENRY  HOLT  &  Co.,  NEW  YORK 
CANADA:  WM.  BRIGGS,  TORONTO 
INDIA  :  R.  &  T.  WASHBOURNE,  LTD. 


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UNIVERSITY 

LIBRARY 

OF 

MODERN  KNOWLEDGE 

Editors  : 

HERBERT   FISHER,  M.A,   F.B.A. 

PROF.   GILBERT  MURRAY,   D.LITT- 
LL.D.,    F.B.A. 

PROF.  J.  ARTHUR  THOMSON,  M.A, 

<  Kb 

p^= 

PROF.   WILLIAM   T.   BREWSTER,  M.A, 
(COLUMBIA  UNIVERSITY,  U.S.A.) 

255=  r                                                          ia 

M                                                                            r1—  

NEW   YORK 

HENRY  HOLT  AND  COMPANY 

THE 

PRINCIPLES  OF 
PHYSIOLOGY 


BY 

JOHN   GRAY  McKENDRICK 

M.D.,    LL.D.,    K.R.S.,    F.Vc.r.E.,    M.R.I. 

Emeritus-Profassor  of  Physiology, 
University  of  Glasgow 


B                                        LONDON 
WILLIAMS    AND    NORGATE 

< 

---,       , 

^. 

6 


PRINTED    BY 

THE    LONDON    AND    NORWICH    PRESS,    LIMITED 
LONDON   AND   NORWICH 


PREFACE 

THIS  is  in  no  sense  a  Text  Book.  It  is  rather 
an  attempt  to  state  the  leading  principles  and 
facts  of  physiology,  and  more  especially  of 
human  physiology,  in  such  a  way  as  will  be 
understood  by  an  intelligent  reader  who  has 
had  no  special  scientific  training.  If  the 
perusal  of  this  little  book  leads  the  reader 
to  wish  to  know  more  of  this  fascinating 
science,  which,  in  a  sense,  is  the  meeting-point 
of  many  sciences,  he  is  referred  to  the  Bib- 
liography, and  the  aim  of  the  writer  will  be 
accomplished. 

J.  G.  M. 
MAXIEBURN, 
STONEHAVEN, 
January,  1912. 


252437 


CONTENTS 

CHAPTER 

I    PHYSIOLOGY,     ITS     SCOPE,     AIMS,     AND 

RELATION  TO  OTHER  SCIENCES          .  9 

II    THE    CHARACTERISTICS    OF    LIVING    OR- 
GANISMS          20 

III  THE  ACTIVITIES  OF  LIVING  BEINGS.         .        30 

IV  ORIGIN     AND     DEVELOPMENT    OF    THE 

INDIVIDUAL    .....        37 

V    THE    DEVELOPMENT    OF    TISSUES    AND 

ORGANS 55 

VI    MATTER   AND    ENERGY   IN   THE    LIVING 

BODY,  CHEMICAL  PROCESSES   .         .        65 

VII    INCOME    OF    MATTER,    ABSORPTION    OF 

FOOD -STUFFS  .....        90 

VIII    THE  BLOOD  :    ITS  RELATION  TO  LIVING 

TISSUES 109 

IX    THE  OUTPUT  OF  WASTE  MATTER     .         .       125 

X    HIDDEN     PROCESSES      AND      ULTIMATE 

PHENOMENA  OF  NUTRITION      .         .       144 

XI    THE  LIBERATION  OF  ENERGY  .         .       161 

XII    THE  REGULATING  MECHANISM.    NERVOUS 

SYSTEM  ...         69 


8  CONTENTS 

CHAPTER  PAGE 

XIII  RELATION  TO  THE   OUTER  AND   INNER 

WORLDS  BY  THE  SENSES          .        .  214 

XIV  THE  VOICE 226 

XV    DEATH 235 

XVI    PHILOSOPHICAL    REFLECTIONS.    THE 

TREND  OF  PHYSIOLOGY  .        .        .  239 

XVII    BIBLIOGRAPHY 243 

GLOSSARY 245 

HISTORICAL  NOTES        ....  25? 

INDEX           ....  255 


THE    PRINCIPLES    OF 
PHYSIOLOGY 

CHAPTER    I 

ITS  SCOPE,  AIMS  AND  RELATIONS 

1.  PHYSIOLOGY  is  the  science  which  describes 
and  endeavours  to  explain  the  phenomena 
manifested  by  living  beings.  It  may  also  be 
said  to  treat  of  the  changes  that  occur  in 
living  matter.  It  deals  with  that  special 
mode  of  activity  we  call  Life. 

2.  Living  beings  are  divided  into  plants 
and  animals.  There  are  many  forms  difficult 
to  classify  ;  these  seem  to  belong  to  either  the 
plant  or  the  animal  world,  according  to  the 
point  of  view  from  which  we  regard  them. 
All  living  things,  however,  show  certain 
general  characters,  by  which  we  know  they 
are  alive.  They  are  developed  from  a  parent 

or  parents,   they  require  food  and  oxygen, 
9 


10     PRINCIPLES   OF  PHYSIOLOGY 

they  pass  through  a  number  of  stages  in  their 
existence,  they  reproduce  their  kind,  and  they 
die.  It  may  not  always  be  easy  to  observe 
some  of  these  phenomena  in  the  lower  forms, 
but  we  find  that  their  bodies  are  composed  of 
matter  that  possesses  certain  properties,  and 
we  characterize  such  matter  as  being  alive. 

3.  One  of  the  lessons  of  scientific  investiga- 
tion is  that  in  the  study  of  phenomena  we  find 
transition — a  series  of  changes,  and  the  gradual 
passage  of  one  state  into  another — while  a 
superficial  examination  may  appear  to  establish 
clear  lines  of  division  between  different  depart- 
ments of  knowledge.  Thus  we  distinguish 
between  that  which  we  say  is  dead  matter, 
and  that  which  we  consider  to  be  alive. 
More  careful  examination,  however,  shows 
that  certain  properties  may  be  the  same,  or 
similar,  in  both  dead  and  living  matter.  Thus 
a  crystal,  which  we  regard  as  dead,  grows 
and  increases  in  size  in  accordance  with 
physical  laws.  Living  matter  also  grows  and 
increases  in  size,  but  by  a  different  process 
from  that  of  a  crystal.  So  that  mere  increase 
in  size,  in  certain  conditions,  may  characterize 


SCOPE  AND  AIMS  11 

both  that  which  is  dead  and  that  which  is 
alive.  Changes  even  in  the  minute  structure 
of  both  dead  and  living  matter  may  occur. 
For  example,  it  is  known  that  slow  changes 
may  happen  in  the  structure  of  even  hard 
metals.  Particles  of  gold  may  penetrate 
into  a  mass  of  solid  lead,  and  solid  bodies 
may  even,  by  slow  movements,  sink  into  an 
apparently  brittle  mass  of  cobblers'  wax. 
Slow  changes  probably  occur  in  all  kinds  of 
matter,  even  the  most  dense  and  durable. 
Thus  molecular  changes,  or,  in  other  words, 
movements,  may  occur  in  matter  which  we 
call  dead.  Molecular  movements  also  occur 
in  living  matter,  so  that  such  minute  move- 
ments do  not  enable  us  to  distinguish  between 
what  is  dead  and  what  is  alive.  Both  dead 
and  living  matter,  again,  are  subject  to  the 
laws  of  gravitation,  and  many  electrical  and 
optical  phenomena  are  manifested  in  a 
similar  way  by  so-called  dead  and  by  so-called 
living  matter. 

4.  There  is  no  difficulty,  however,  in  recog- 
nizing many  of  the  phenomena  of  life  in  one 
of  the  higher  forms,  whether  it  be  a  plant 


12     PRINCIPLES  OF  PHYSIOLOGY 

or  an  animal.  Thus  one  of  the  higher  plants 
is  rooted  to  the  soil,  from  which  it  mainly 
derives  nourishment ;  it  spreads  its  branches 
and  leaves  and  flowers  to  the  air,  and  it 
breathes.  An  animal  of  the  higher  orders 
shows  active  movements  such  as  running  or 
leaping,  it  breathes,  it  requires  food,  and  it 
can  produce  heat.  We  find  accordingly  that 
there  are  phenomena  to  be  observed  and 
explained  in  both  the  plant  and  the  animal. 
It  is  the  province  of  the  physiologist  to  study 
those  phenomena  and  to  offer  explanations. 
The  field  of  work,  however,  is  so  immense  that 
the  science  naturally  subdivides  into  plant  and 
animal  physiology.  The  first  is  a  division  of 
the  science  of  Botany,  while  that  of  the  latter 
falls  into  the  domain  of  the  Zoologist.  Thus, 
in  a  sense,  all  the  phenomena  of  living  things 
fall  into  those  two  sciences,  but,  by  common 
consent,  the  task  of  describing  and  explaining 
the  phenomena  on  which  life  depends,  is 
relegated  to  physiology,  and  this  again  may  be 
subdivided  into  the  physiologies  of  the  various 
animals.  We  discuss  the  phenomena  occur- 
ring in  the  body  of  man  as  Human  Physiology, 


SCOPE  AND   AIMS  13 

but  we  might  equally  well  discuss  the  physi- 
ology of  the  domestic  animals,  such  as  that 
of  the  horse  or  ox,  or  the  physiology  of  birds, 
or,  indeed,  of  any  group  of  animals.  It  is 
found  that  no  sufficient  explanation  of  many 
vital  phenomena  can  be  given  by  the  study 
of  one  animal,  or  group  of  animals,  and 
accordingly  knowledge  may  be  brought  to  a 
focus  in  the  department  of  science  called 
Comparative  Physiology. 

At  one  time  the  word  physiology  expressed 
all  that  we  now  term  physics  (phusis,  nature, 
logos,  a  description),  a  description  of  natural 
phenomena  in  general.  For  many  years, 
however,  its  meaning  has  been  limited  to  the 
discussion  of  phenomena  as  these  occur  in 
living  beings. 

5.  But  all  science  is  in  a  sense  one,  and 
accordingly  we  find  that  the  compartments  of 
knowledge  we  call  the  sciences  are  related  to 
each  other.  Physiology  is  closely  related  to, 
and  largely  depends  on,  three  sciences : 
Anatomy,  Physics  and  Chemistry.  A  general 
acquaintance  with  these  sciences  is  of  para- 
mount importance  to  any  one  about  to  enter 


14     PRINCIPLES    OF   PHYSIOLOGY 

on  the  study  of  physiology.  One  should  know 
something  of  the  plan  of  structure  met  with 
in  the  great  subdivisions  of  the  animal  kingdom. 
The  student  of  human  physiology,  for  exam- 
ple, should  be  acquainted  with  the  general 
anatomy  of  the  human  body,  and  of  its  various 
organs,  although  much  may  be  learned  from 
the  dissection  of  one  of  the  lower  mammals, 
such  as  the  rabbit.  Not  only  is  it  necessary 
to  study  the  forms  and  relations  to  other 
parts  of  the  various  organs,  as  seen  by  the 
naked  eye,  but  also  the  minute  structure  of  the 
organs  and  tissues  as  revealed  by  the  micro- 
scope, and  by  modern  technical  methods  of 
preparing  these  for  examination.  This  is  the 
department  known  as  Histology,  a  depart- 
ment of  science  that  in  recent  years  has  made 
enormous  progress.  The  demands  of  one 
science  stimulate  another,  and  we  find  an 
example  in  the  development  of  the  modern 
microscope,  which,  both  in  its  mechanical  and 
optical  arrangements,  may  be  regarded  as  a 
nearly  perfect  scientific  instrument.  The 
methods  of  hardening,  cutting  into  thin 
sections,  and  staining  by  various  colouring 


SCOPE   AND   AIMS  15 

matters  are  now  highly  skilful  and  accurate. 
Histology  has  both  a  morphological  side,  in 
as  far  as  it  deals  with  form,  and  a  physiological 
when  it  treats  of  the  functions  performed  by 
these  tissues.  Further,  much  information  is 
furnished  to  the  physiologist  by  the  examina- 
tion of  the  body  at  various  stages  of  growth, 
and  more  especially  in  the  earlier  stages. 
Thus  the  study  of  the  formation  and  early 
development  of  the  embryo,  and  tracing  the 
origin  of  the  tissues,  and  the  gradual  building 
up  of  the  more  complicated  organs,  have  > 
thrown  light  on  vital  phenomena.  This  line  ' 
of  research  is  known  as  Embryology. 

The  body  is  also  the  theatre  of  many 
phenomena  of  a  chemical  character ;  indeed 
it  may  be  said  that  the  phenomena  of  life 
depend  essentially  on  chemical  changes.  As 
we  shall  see,  food  and  oxygen  are  introduced 
into  the  body,  and,  by  chemical  changes, 
often  of  a  complicated  kind,  many  chemical 
substances  are  formed,  some  of  which  are  built 
into  the  tissues,  while  others  are  thrown  out 
as  effete.  Many  of  the  operations  in  the 
digestion  of  food  and  in  the  formation  of 


16     PRINCIPLES   OF  PHYSIOLOGY 

substances  in  the  blood  are  purely  chemical. 
Physiological  Chemistry  has  as  its  field  a 
description  of  the  physical  and  chemical  char- 
acter of  the  substances  forming  the  tissues 
and  existing  in  the  fluids  of  the  body.  It 
also  gives  an  explanation  of  the  chemical 
processes  occurring  in  the  body.  This  depart- 
ment of  science  has  also  made  great  progress 
in  recent  years.  At  one  time  it  was  thought 
that  certain  substances  formed  in  the  body 
could  be  formed  only  in  living  matter.  The 
synthesis  of  urea  by  Wohler  in  1828  upset  this 
notion.  This  experiment  laid  the  foundations 
of  organic  chemistry.  Since  then  hundreds  of 
chemical  substances  found  in  plant  or  animal 
tissues  have  been  formed  synthetically  by  the 
chemist  by  the  operation  of  chemical  methods. 
It  is  remarkable,  however,  that  in  living  matter 
such  substances  are  formed  by  molecular 
action  and  by  hidden  processes,  while  the 
chemist  can  only  form  them  by  the  agency 
of  high  temperatures,  and  the  action  of  power- 
ful substances  such  as  acids  or  oxydising  or 
reducing  substances.  It  is  possible  that  the 
processes  of  nature  and  of  the  chemist  may  in 


SCOPE  AND  AIMS  17 

essence  be  identical,  or  at  all  events  similar, 
but  this  is  doubtful. 

6.  The  laws  of  physics  are  applied  by  the 
physiologist  to  the  investigation  of  the 
motions  of  the  solids  and  fluids  in  the  animal 
organism.  Thus  the  movements  of  the  limbs 
in  locomotion  are  mechanical,  the  movements 
of  the  blood  in  the  circulation  are  subject  to 
the  physical  laws  of  hydrodynamics,  the 
interchanges  of  gases  between  the  air  and 
the  blood  in  respiration  are  to  be  explained 
as  special  cases  of  the  transfusion  of  gases 
through  thin  membranes,  while  the  actions 
of  the  eye  and  ear  can  only  be  understood 
by  the  study  of  optics  and  acoustics  and 
their  application  to  these  highly  specialized 
mechanisms.  The  absorption  into  the  blood 
of  nutrient  matters,  after  their  preparation  by 
digestion,  and  the  elimination  of  waste  matters 
from  the  blood  by  various  organs,  are  so  far 
to  be  explained  by  the  laws  regulating  the 
passage  of  fluids  through  thin  membranes, 
and  which  are  studied  by  the  physicist. 
It  may  indeed  be  said  that  physical  processes 
are  more  or  less  involved  in  all  the  phenomena 
B 


18     PRINCIPLES  OF  PHYSIOLOGY 

of  living  matter.  It  would  also  seem  that 
electricity  plays  an  important  part  in  vital 
activities,  or,  at  all  events,  it  is  intimately 
related  to  the  intricate  and  hidden  molecular 
phenomena  on  which  life  depends.  Finally, 
the  phenomena  of  the  living  being  can  only 
be  accounted  for  by  their  consideration  in  the 
light  of  the  modern  doctrine  of  the  conserva- 
tion of  energy,  a  doctrine  which  may  be  said 
to  have  originated  in  the  study  of  these 
phenomena.  The  history  of  this  great  idea 
shows  that  the  endeavour  to  account  for 
animal  heat  and  the  relation  of  food  and 
oxygen  to  the  production  of  heat  and  of 
animal  movements,  was  one  of  the  first  steps 
towards  the  building  up  this  doctrine,  which 
lies  at  the  foundation  of  all  physical,  chemical 
and  biological  science. 

7.  Thus,  physiology  rests  on  a  tripod  of 
three  sciences — Anatomy,  Chemistry,  and 
Physics.  It  brings  to  bear  on  its  problems 
all  the  information  that  can  be  gathered  from 
those  sciences,  considered  in  their  broadest 
relations,  and  while  physiology  has  its  own 
methods,  it  may  be  said  to  be  the  mechanical 


SCOPE  AND  AIMS  10 

and  chemical  interpretation  of  phenomena 
happening  in  living  matter.  We  shall  see, 
however,  that  in  the  present  state  of  the 
science  there  are  not  a  few  phenomena  which 
cannot  be  so  explained.  Such  phenomena 
are  provisionally  termed  vital.  Meantime 
we  may  note  that  as  physiological  science 
advances,  vital  phenomena  are  more  and 
more  regarded  as  special  examples  of  the 
operation  of  chemical  and  physical  laws. 
Still  there  are  at  present,  and  it  is  not  going 
too  far  to  assert  that  there  must  always  be, 
some  phenomena  that  cannot  be  so  explained. 
Thus  it  would  appear  to  be  impossible  ever  to 
account  for  feeling,  willing,  thinking,  and  other 
mental  (psychical)  states  or  processes  by  any 
purely  physical  or  chemical  operations. 


CHAPTER    II 

THE   CHARACTERISTICS   OF   LIVING   ORGANISMS 

CERTAIN  of  these  have  already  been  referred 
to.  We  may  now  consider  some  of  the 
characteristics  of  living  beings  more  fully. 

8.  Physical  structure.  No  living  matter 
ever  assumes  a  crystalline  form,  but  crystals 
may  be  imbedded  in  it.  Living  matter  is 
always  soft,  jelly-like,  diffluent,  readily  per- 
meated by  water,  oxygen,  and  the  crystalloids. 
It  is  matter  in  a  colloidal  state,  which,  as  it 
permits  of  the  free  play  of  molecular  inter- 
changes, has  been  termed  a  dynamical  state 
of  matter.  The  colloidal  shape  is  not,  however, 
peculiar  to  living  matter,  as  it  is  shown  by 
certain  conditions  of  silicic  acid,  peroxide  of 
iron,  etc.  The  firmer  portions  of  living  matter 
are  always  soft ;  they  readily  absorb  water 
by  imbibition.  It  has  been  supposed  that 
living  matter  consists  of  still  more  minute 
20 


LIVING  ORGANISMS  21 

particles,  possibly  of  irregular  form,  and  that 
water  fills  up  the  spaces  between  such  particles. 
Such  molecules  are  assumed  to  be  in  a  state 
of  incessant  movement,  and  these  movements 
are  associated  with  the  absorption  and  libera- 
tion of  water.  A  watery  consistence  is 
essential  to  the  phenomena  of  life.  Move- 
ments of  minute  particles  of  matter  in  a 
fluid  are  well  illustrated  by  the  Brownian 
movements  seen  under  the  microscope,  magni- 
fying say  250  diameters,  if  we  squeeze  and 
examine  a  little  bit  of  fresh  vegetable  tissue. 
The  minute  particles  are  seen  to  be  in  a  state 
of  incessant  vibration. 

9.  Chemical  composition.  Of  the  seventy 
elements  known  to  chemists  only  from  eighteen 
to  twenty  have  been  found  in  living  matter, 
and  of  these  the  chief  are  oxygen,  hydrogen, 
nitrogen  and  carbon.  With  these  are  asso- 
ciated, of  the  non-metals,  sulphur,  phosphorus, 
and  chlorine ;  of  the  alkalies,  sodium  and 
potassium;  of  the  alkaline  earths,  calcium 
and  magnesium  ;  and  of  the  metals  only  one, 
iron.  Minute  quantities  of  other  substances 
have  been  found,  such  as  argon,  silicon, 


22     PRINCIPLES   OF   PHYSIOLOGY 

fluorine,  iodine,  bromine,  manganese,  and 
copper,  but  the  presence  of  some  of  these  sub- 
stances may  be  accidental.  It  should  be  noted 
that  carbon  and  nitrogen,  along  with  hydrogen 
and  oxygen,  are  essential  to  life.  Oxygen  and 
hydrogen  are  often  in  the  proportions  that  form 
water — 2  of  hydrogen  to  1  of  oxygen.  From 
these  elements  complex  chemical  substances 
are  built  up.  Thus  the  living  matter  in  the 
cells  of  a  plant,  mainly  under  the  stimulus 
of  light,  so  combines  carbon,  hydrogen  and 
oxygen  as  to  form  starches,  sugars,  and  fats  ; 
and  it  may  also  form  still  more  complex 
chemical  substances,  known  as  proteins, 
which  contain  carbon,  hydrogen,  and  oxygen, 
and  the  all  important  element  nitrogen. 
Such  bodies,  often  termed  proximate  prin- 
ciples, thus  formed  in  a  plant,  may  become 
the  food  of  an  animal  and  be  built  into  its 
tissues,  or  be  directly  used  up  in  various 
transformations  connected  with  vital  activity. 
The  term  proximate  principle  was  given  by 
the  earlier  physiological  chemists,  because  they 
thought  that  certain  substances,  such  as  the 
proteins  (albumen,  etc.)  existed  in  the  tissues 


LIVING  ORGANISMS  23 

or  fluids  as  they  were  known  to  the  chemist. 
We  now  know  that  this  is  an  assumption. 
These  so-called  principles  probably  only  arise 
from  the  decomposition  of  matter  that  was 
once  alive.  One  of  the  characteristics  of 
these  complex  organic  substances,  whether 
as  found  in  the  bodies  of  plants  or  animals, 
is  their  instability.  They  are  liable  to  split 
up  into  simpler  bodies,  and  this  splitting  up 
is  always  associated  with  the  liberation  of 
energy,  chiefly  as  heat  or  movement.  Thus, 
in  living  matter  two  apparently  opposite 
chemical  processes  are  continually  at  work ; 
there  is  either  the  building  up  of  simpler 
substances  into  more  complex  ones,  such  as  the 
formation  of  starch  from  the  elements  carbon, 
hydrogen,  and  oxygen,  or  the  pulling  down  of 
complex  substances  into  simpler  ones,  as  the 
resolution  of  starch  into  carbonic  acid  and 
water.  In  the  upbuilding  process,  often  termed 
anabolic,  energy  is  locked  up,  or  becomes 
latent,  while  in  the  pulling  down  process, 
termed  katdbolic,  energy  is  liberated  and 
becomes  kinetic.  Thus  starch  (or  oil),  when 
burnt,  that  is  oxidised,  yields  carbonic  acid 


24     PRINCIPLES   OF  PHYSIOLOGY 

and  water,  and  energy  is  liberated  as  heat, 
which  may  be  transformed  into  the  motion 
of  a  steam  engine  and  caused  to  do  work. 
Living  matter  is  thus  continually  undergoing 
a  series  of  chemical  changes  of  composition 
and  decomposition,  as  a  result  of  which  there 
is  an  incessant  renovation  of  its  particles. 
It  would  appear  that  chemical  changes  are  a 
necessary  condition  of  the  action  of  living 
matter ;  part  of  the  living  matter  dies,  is 
decomposed,  or  rather,  its  decomposition  is 
coincident  with  its  death,  and  the  dead  matter 
is  thrown  out  of  the  body.  New  matter  is 
then  added  from  the  outer  world.  There  is 
thus  a  perpetual  exchange  between  the  dead 
and  the  living  worlds,  which  may  be  termed  a 
circulation  of  matter  between  the  dead  and  the 
living.  Portions  of  the  earth's  surface  now  dead 
were  once  part  of  the  bodies  of  living  beings, 
and  may  again  enter  into  the  living  state. 

10.  Form  and  Mode  of  Growth.  As  already 
pointed  out,  living  matter  is  jelly-like  in  its 
consistence.  It  often  changes  its  form,  as 
may  be  seen  in  an  amoeba  or  in  the  colourless 
cells  in  the  blood.  At  the  beginning  of 


LIVING   ORGANISMS  25 

existence,  the  typical  form  is  nearly  spherical, 
as  seen  in  the  ovum,  and  also  in  many  of  the 
minute  cells  of  which  the  body  is  composed. 
Living  matter  never  assumes  crystalline  forms; 
it  does  not  grow  like  a  crystal,  by  the  deposition 
of  new  matter  on  its  surfaces,  but  by  absorbing 
matter  into  its  substance  and  usually  trans- 
forming this  into  matter  like  itself.  A  crystal 
does  not  transform,  and  it  grows  by  the 
deposition  of  new  layers  on  its  surface ; 
living  matter  can  transform,  or  assimilate, 
and  it  can  grow  by  the  transformed  matter 
becoming  part  of  its  substance.  It  is  re- 
markable, however,  that  dead  matter  may 
assume  forms  very  similar  to  the  forms  of 
living  matter.  In  certain  media  crystallisable 
substances  may  take  on  organic  shapes,  and 
various  mixtures  of  soaps,  gums,  etc.,  may 
form  a  froth  which,  under  the  microscope,  may 
show  forms  very  similar  to  that  seen  in  living 
stuff.  In  some  circumstances  even  the  move- 
ments of  living  matter  may  be  imitated. 
Thus,  a  highly  complex  substance  called 
protagon  can  be  extracted  from  yolk  of  egg 
by  hot  alcohol.  If  a  minute  portion  be 


26     PRINCIPLES   OF   PHYSIOLOGY 

placed  under  the  microscope  and  a  drop  of 
water  be  allowed  to  impinge  on  the  edge  of  the 
morsel,  curious  twisted  or  spiral  structures 
may  be  seen  shooting  out.  These  myelin 
forms,  as  they  are  called,  are  instructive,  as 
showing  lifelike  movements  in  dead  matter — 
depending  on  changes  in  surface  tension. 
Some  have  even  asserted  that  living  matter  is 
essentially  a  kind  of  froth,  and  that  the 
structural  forms  are  similar  to  those  seen 
when  one  blows  a  mass  of  soap  bubbles 
Walls  and  partitions  may  then  appear, 
and  even  one  part  may  seem  to  be  within 
another,  not  unlike  certain  structures  seen 
in  a  thin  section  of  living  matter.  Such 
imitation- 'forms,  however,  do  not  imply  life. 
11.  Evolutional  History.  A  living  being, 
during  the  course  of  its  existence,  passes 
through  phases  that  follow  each  other  in  a 
certain  order.  It  originates  in  a  germ  which  is 
developed  in  a  parent,  that  is,  in  a  previously 
existing  being  that  has  essentially  the  same 
structure  and  properties.  This  germ,  which 
is  known  as  the  spore,  seed,  or  egg  of  plants 
and  animals,  is  a  cell,  a  comparatively  simple 


LiVING   ORGANISMS  27 

structure.  After  its  separation  from  the 
parent  body,  it  is  capable  of  independent  exist- 
ence, and,  under  favourable  circumstances, 
of  developing  into  a  new  individual,  in  most 
respects  similar  to  that  from  which  it  derived 
its  origin  Living  beings  form  a  continuous 
series,  from  the  first  appearance  of  life  on  the 
earth  until  now.  The  offspring  have  usually 
characters  which  they  have  inherited  from 
their  parents,  but  they  may  develop  new 
characters  which  may  arise  from  new  cir- 
cumstances affecting  them  during  their  own 
lives.  If  these  characters,  either  inherited 
or  acquired,  are  transmitted  to  descendants, 
the  phenomenon  is  known  as  heredity.  Each 
living  being  shows  a  period  during  which 
there  is  a  maximum  vital  activity,  when  the 
liberation  of  energy  is  greatest.  During  life 
it  passes  by  stages  up  to  this  period ;  then, 
after  a  stage  of  maximum  activity,  the 
powers  of  the  organism  slowly  decline. 
During  its  life  an  organism  undergoes  change 
of  form,  there  is  increase  of  mass,  and  it  shows 
increasing  complexity  of  structure.  These 
changes,  however,  do  not  go  on  indefinitely. 


28     PRINCIPLES   OF   PHYSIOLOGY 

A  condition  of  fully  developed  organization 
is  reached,  for  each  kind  of  living  thing, 
reproductive  processes  occur,  the  processes 
of  life  go  on  more  slowly  and  less  completely, 
and  finally  some  part  of  the  machinery  of 
life  breaks  down,  and  death  occurs.  This  is 
the  last  stage  in  the  evolution  of  that  particular 
organism.  After  death  of  the  tissues  of  the 
body,  it  is  submitted  to  the  action  of  external 
agencies,  both  physical,  chemical,  and  vital 
(the  vital  being  due  to  the  activities  of 
micro-organisms  of  an  inferior  order),  and 
these  ultimately  reduce  it  to  the  simple 
elements  of  which  the  body  was  at  first  com- 
posed. 

12.  A  living  being  is  affected  during  every 
moment  of  its  life  by  the  medium  in  which  it 
lives.  The  medium  furnishes  the  material 
necessary  for  its  existence.  Dead  matter  is 
supplied  to  take  the  place  of  the  living  matter 
that  has  died  after  having  done  its  work. 
External  modes  of  energy,  such  as  heat,  light, 
and  electricity,  act  upon  it,  and  energy  is 
supplied  also  by  the  chemical  changes  brought 
about  ultimately,  but  by  many  subsidiary 


LIVING  ORGANISMS  29 

processes,  by  the  interaction  of  the  elements  of 
food  and  of  the  oxygen  of  the  air.  There  is 
thus  action  and  reaction  between  the  living 
being  and  the  conditions  in  which  it  lives. 
These  conditions  are  termed  the  environment. 
The  living  being  has,  within  limits,  the  faculty 
of  suiting  itself  to  the  surrounding  conditions. 
Such  a  power,  which  is  a  necessary  condition 
of  the  existence  of  every  living  being,  is  known 
as  its  variability.  It  is  the  power  of  adaptation 
to  external  conditions. 


CHAPTER    III 

THE    ACTIVITIES    OF   LIVING    BEINGS 

13.  LIFE  is  a  condition  of  activity.  In  the 
body  of  one  of  the  higher  animals  we  see 
activities  manifested  in  various  forms.  Some 
of  these  have  already  been  referred  to,  but  we 
must  now  give  a  statement  of  those  which 
it  is  the  special  province  of  the  physiologist 
to  explain. 

(1)  Animal  Heat.  The  body  of  an  animal 
(we  may  leave  plants  out  of  this  discussion, 
although  much  that  will  here  be  indicated 
also  applies  to  them)  has  a  certain  mean 
temperature.  In  so  called  warm-blooded 
animals,  such  as  the  birds  and  mammals, 
the  temperature  of  the  body  varies  only 
through  a  few  degrees,  even  although  there 
may  be  very  considerable  variations  in  the 
temperature  of  the  surrounding  medium. 
Thus  the  temperature  of  the  body  of  a  man, 

30 


ACTIVITIES  OF  LIVING  BEINGS    31 

taken  by  a  suitable  thermometer  placed  for 
a  few  minutes  in  the  arm-pit,  varies  in  a 
state  of  health  only  within  a  few  fractions  of 
a  degree  above  or  below  98°  Fahr.  whether 
the  temperature  be  taken  within  the  Arctic 
circle  or  at  the  Equator.  On  the  other  hand, 
the  temperature  of  the  body  of  a  frog  or  of  a 
fish  varies  as  the  surrounding  temperature 
rises  and  falls.  Such  an  animal  is  said  to 
be  cold-blooded.  The  terms  cold-blooded 
and  warm-blooded  are  not  scientifically 
appropriate.  A  warm-blooded  animal,  such 
as  a  man  or  a  dog,  has  a  temperature  that 
is  fairly  constant,  whereas  a  so-called  cold- 
blooded animal,  like  a  frog  or  a  fish,  has 
a  temperature  that  varies  considerably  with 
the  temperature  of  the  medium  in  which  it 
lives.  But  if  the  temperature  of  the  air 
surrounding  a  man's  body  is  lower  than  98.4° 
F.,  then  the  body  must  be  constantly  losing 
heat  by  radiation  and  conduction.  The 
questions  at  once  arise  :  What  is  the  origin  of 
this  heat  ?  By  what  channels  is  it  lost  from 
the  body  ?  By  what  arrangement  is  the 
temperature  kept  so  uniform  ?  Are  there 


32     PRINCIPLES   OF   PHYSIOLOGY 

heat  regulating  mechanisms  ?  These  ques- 
tions will  be  afterwards  discussed.  It  is  to 
be  noted  that  living  matter  can  only  perform 
its  junctions  within  a  narrow  range  of  tem- 
perature. 

(2)  Motion.  Animals  move  and  parts  of 
their  body  move.  They  leap,  run,  or  walk, 
the  chest  moves  in  respiration,  and  the  heart 
beats.  These  movements  are  accomplished 
rby  the  muscular  tissues,  which  are  the  seat  of 
intense  activities.  Energy  is  here  liberated 
as  motion.  The  physiologist  has  to  study  the 
structure,  nutrition,  and  the  contractile  func- 
tions of  muscular  tissue.  He  finds  that  every 
contraction  of  muscular  tissue  is  associated 
with  active  chemical  changes  occurring  in  the 
tissue,  by  which  there  is  a  breaking  down  of 
muscle  substance,  and  the  formation  of 
chemical  substances  of  a  simpler  nature. 
These  chemical  changes  are  intimately  con- 
nected with  the  breathing  of  the  living  muscle 
substance,  that  is  to  say,  they  depend  on 
chemical  phenomena  in  the  muscle  substance 
which  require  the  presence  of  oxygen  and  lead 
to  the  elimination  of  carbonic  acid  and  of  other 


ACTIVITIES    OF   LIVING  BEINGS     38 

waste  matters.  The  muscle  substance  must  be 
repaired.  This  is  done  by  nutritional  changes 
in  the  muscle.  Materials  are  supplied  in  food, 
which,  after  many  chemical  and  physical 
changes,  are  rebuilt  into  the  muscle  sub- 
stance, thus  renewing  both  the  matter  and 
the  energy  that  have  been  expended  in 
the  muscle  during  its  contractile  activity. 
The  muscle  liberates  energy  as  heat,  motion, 
and,  to  a  small  extent,  under  the  form  of 
electrical  change. 

(3)  Secretion.  This  is  a  peculiar  form  of 
vital  activity  occurring  in  glands,  of  which 
there  are  many  forms.  The  product  of  this 
activity  is  termed  a  secretion.  The  essential 
structures  in  a  gland  are  a  thin  membrane  on 
one  side  of  which  we  find  living  cells,  and  on 
the  other,  and  in  intimate  relation  to  these 
cells,  a  network  of  minute  blood  vessels, 
termed  capillaries.  From  the  capillaries  a 
fluid  exudes  from  the  blood,  and  this  fluid 
supplies  nutrient  material  to  the  living  cells. 
These  cells  take  such  material  into  their  sub- 
stance and  complex  chemical  processes  then 

go  on.     Each  cell  is  a  minute  laboratory  in 

c 


84     PRINCIPLES   OF  PHYSIOLOGY 

which  special  substances  are  formed.  The 
cell  gradually  is  filled  with  these  substances  and 
then  it  bursts,  liberating  its  contents,  or  in 
some  cases  there  seems  to  be  a  gradual  removal 
from  the  cell  of  the  products  of  its  secretion. 
The  matters  thus  collected  from  innumerable 
cells  become  the  secretion  of  the  gland.  We 
may  take  as  an  example  the  secretion  of 
saliva.  The  cells  of  the  salivary  gland  elabor- 
ate the  materials  that  form  the  secretion.  In 
particular,  they  form  a  peculiar  body,  known 
as  ptyalin,  belonging  to  the  class  of  ferments. 
There  is  no  ptyalin  in  the  blood.  It  is  formed 
in  the  cells  of  the  gland.  Nor  is  it  at  once 
formed  from  materials  supplied  by  the  blood. 
There  is  at  least  one  antecedent  substance, 
probably  more  than  one,  marking  stages  in  the 
gradual  formation  of  ptyalin.  In  like  man- 
ner, the  cells  of  the  mammary  gland  elaborate 
the  complex  fluid,  milk,  and  those  of  the 
pancreatic  gland  the  remarkable  bodies  found 
in  the  secretion  of  that  gland,  all  of  which  are 
ferments.  Secretion,  however,  is  essentially 
a  form  of  growth  depending  on  the  activities 
of  the  secreting  celL 


ACTIVITIES  OF  LIVING  BEINGS    35 

(4)  Nervous  activities.  All  the  various  vital 
activities  are  more  or  less  controlled  and 
regulated  by  the  nervous  system,  which  may 
be  regarded  as  the  master  system  of  the  body. 
This  consists  of  the  brain,  spinal  cord,  ganglia, 
and  nerves,  but  it  may  be  more  shortly  de- 
scribed as  formed  of  nerve  centres  and  nerves. 
The  nerves  pass  to  and  from  the  centres, 
connecting  up  all  parts  of  the  body  with  those 
centres.  Nervous  energy  may  originate  in  the 
centres, — brain,  or  cord,  or  ganglia, — and  it 
may  stream  out  along  the  fibres  in  the  nerves 
to  various  organs,  such  as  muscles,  glands, 
blood  vessels,  and,  in  some  animals  (such  as 
the  electric  fishes),  electric  organs.  This 
energy,  as  to  the  nature  of  which  we  know 
little,  awakens  the  activities  of  those  organs. 
Under  its  influence,  muscular  fibres  will 
contract,  the  cells  of  a  gland  will  secrete, 
the  walls  of  small  vessels  will  alter  their 
calibre,  and  an  electric  organ  will  be  the  seat 
of  electrical  changes.  The  centres,  in  their 
turn,  receive  from  the  periphery  of  the  body, 
from  the  sense  organs,  and  from  all  other 
organs,  nervous  impulses  that  awaken  activi- 


36     PRINCIPLES   OF   PHYSIOLOGY 

ties  in  the  centres.  These  activities  may 
cause  other  impulses  to  stream  outwards  to 
the  various  organs  and  thus  stimulate  them, 
or  they  may,  as  in  the  higher  brain  centres, 
be  associated  with  various  states  of  con- 
sciousness, such  as  sensations,  emotions  or 
intellectual  and  volitional  processes.  Thus 
the  whole  body  is  bound  together,  and  controlled 
and  regulated,  by  the  nervous  system. 


CHAPTER    IV 

ORIGIN    AND    DEVELOPMENT    OF   THE 
INDIVIDUAL 

14.  AFTER  a  general  survey  of  some  of  the 
fundamental  characteristics  of  living  beings,  we 
now  turn  our  attention  more  especially  to  the 
physiology  of  man,  and  the  first  question  that 
naturally  presents  itself  is — How  does  he, 
as  an  individual,  originate  ?  At  once  the 
answer  will  be  given  that  he  springs  from 
parents,  a  mother  and  a  father.  This  easy 
answer,  however,  gives  no  information,  and 
one  may  be  rather  startled  by  the  statement 
that  he  springs  from  structures  of  micros- 
copical dimensions,  that  he  owes  his  origin 
to  the  combination  of  an  egg  or  ovum  with 
a  body  called  a  spermatozoon.  In  this 
he  resembles  the  great  majority  of  living 
things.  To  appreciate,  however,  the  wonder- 
ful story  of  how  this  comes  about,  it  is  neces- 

37 


38     PRINCIPLES   OF  PHYSIOLOGY 

sary  to  fix  our  attention  on  what  is  known  as 
a  cel^  the  first  and  smallest  unit  of  structure 
from  which  the  tissues  of  the  body  are  formed. 
If  we  examine  the  body,  say  of  a  rabbit,  we  find 
it  is  built  up  of  various  tissues.  Thus  we  find 
the  flesh,  consisting  chiefly  of  muscular  tissue, 
the  cartilages  or  gristles,  the  bones,  the  brain 
and  structures  related  to  it  (constituting  the 
nervous  system),  and  the  various  glands  and 
internal  organs,  such  as  lungs,  stomach  and 
liver.  But  if,  by  appropriate  methods,  such 
as  are  used  in  the  examination  of  tissues  and 
organs  by  the  microscope,  we  pursue  the 
analysis  farther,  and  more  especially  if  we 
study  the  tissues  at  various  periods  in  their 
development,  we  find  that  they  all  originate 
from  cells.  A  cell  is  a  small  bag  or  vesicle, 
varying  in  size  from  the  1/6000  of  an  inch 
to  bodies  just  visible  to  the  naked  eye.  Ante- 
cedent even  to  cells,  there  is  a  still  more 
primitive  substance  known  as  protoplasm. 
It  is  a  jelly-like,  colourless,  or  faintly  yellow 
substance,  having  often  embedded  in  it 
minute  granules.  It  may  either  form  large 
masses,  as  in  certain  fungus-like  forms,  or  it 


ORIGIN  AND   DEVELOPMENT      39 

may  be  in  small  portions,  like  the  well-known 
amoeba  found  in  stagnant  pools.  One  of  its 
most  remarkable  characteristics  is  that  of 
free  movement,  by  which  it  may  change  its 
shape  from  time  to  time.  It  has  the  power  also 
of  absorbing  organic  matter  from  the  medium 
in  which  it  lives,  and  of  converting  this  into 
protoplasm.  It  breathes  :  using  up  oxygen 
and  producing  carbonic  acid. 

Protoplasm  is  always  a  constituent  of 
living  cells.  A  cell  may  consist  simply  of  a 
bit  of  protoplasm,  or  it  may  consist  of  proto- 
plasm having  embedded  in  it  a  minute  more 
or  less  globular  body  known  as  a  nucleus, 
or  it  may  have  a  thin  envelope  surrounding  it 
called  the  cell  wall.  A  typical  cell,  therefore, 
consists  of  a  cell-wall,  the  protoplasmic 
contents  of  the  cell,  and  a  nucleus.  It  can  be 
shown  that  the  cell  substance  (or  cytoplasm), 
and  also  the  nucleus,  often  show  a  network  of 
very  fine  fibres  or  a  coiled  fibre,  and  that  the 
contents  are  not  structureless,  as  was  at 
one  time  supposed.  The  minute  fibres,  or 
portions  of  fibres,  found  in  the  nucleus  have 
a  special  significance.  These  take  up  certain 


40     PRINCIPLES  OF  PHYSIOLOGY 

stains  readily,  and  the  material  forming  them 
is  termed  chromatin  or  colourable  stuff. 
Further,  the  minute  bodies  thus  stainable  are 
termed  chromosomes,  and  it  is  remarkable  that 
the  number  of  chromosomes  is  almost  invaria- 
bly the  same  for  the  cells  of  each  species  of 
animal.  The  cell  also  contains  matter  that 
is  not  stainable,  or  achromatin,  as  well  as 
matters  formed  from  the  substance  of  the 
cells,  such  as  droplets  of  fat,  granules  of  a 
starchy  substance  called  glycogen,  and  other 
bodies,  as  in  secreting  cells  already  mentioned. 
There  is  usually  a  layer  of  absolutely  struc- 
tureless matter  next  the  cell  wall  termed 
hyaloplasm ;  and  it  can  be  shown  that  certain 
matters  may  pass  through  this  layer  while 
others  cannot  do  so.  This  is  of  importance 
in  connection  with  absorption  of  matters  by 
the  cell  and  the  elimination  of  matters  from  it 
It  is  important  to  note  that  the  cell  is  the 
theatre  of  activities,  of  a  physical,  chemi- 
cal, and  vital  nature,  and  that  probably 
all  the  phenomena  of  life  may  be  manifested 
by  a  cell.  It  often  shows  irritability,  or  the 
power  of  responding  to  a  stimulus,  a  property 


ORIGIN  AND   DEVELOPMENT      41 

which  may  be  the  beginning  of  psychical 
states.  These  activities  are  all  more  or  less 
controlled  and  regulated  by  the  nucleus.  If  a 
cell  be  divided  artificially  so  that  one  portion  of 
the  protoplasm  contains  the  nucleus,  while 
the  other  has  no  nucleus,  the  latter  portion 
soon  dies,  but  the  other  portion  remains  alive, 
and  may  grow  and  perform  its  functions  as 
before.  Cells  apparently  secrete  certain  mat- 
ters which  collect  outside  the  cells,  forming 
intercellular  matter,  so  as  to  form  a  tissue, 
such  as  cartilage  or  gristle  ;  in  other  cases, 
this  intercellular  matter  may  form  a  fibrous 
structure  impregnated  with  earthy  matter, 
as  in  bone ;  or  the  cells  themselves  may 
be  modified  so  as  to  form  more  complicated 
tissues,  such  as  muscle ;  or  the  cells  may  cover 
such  surfaces  as  the  skin,  or,  as  secreting  cells, 
line  the  pouches  of  glands.  All  tissues  are 
primarily  formed  of  cells,  and  the  activities  of 
these  tissues  are  the  sum  of  the  activities  of 
the  cells.  All  cells  arise  from  cells.  Omnis 
cellula  e  cellula. 

15.  The  formation  of  the  body  is  the  result 
of  the  union  of  two  primitive  cells,  an  ovum, 


42     PRINCIPLES   OF   PHYSIOLOGY 

or  egg,  derived  from  a  female,  and  a  sper- 
matozoon, derived  from  a  male  parent.  The 
ovum  is  a  small  spherical  vesicle  about  1  /1 00 
of  an  inch  in  diameter.  Imbedded  in  its 
protoplasm  there  is  a  large  spherical  nucleus, 
termed  the  germinal  vesicle,  and,  in  the  nucleus, 
there  is  a  still  smaller  body,  the  germinal 
spot.  Both  the  cell  protoplasm  and  the 
nucleus  show  a  network  of  fine  fibres,  and  in 
the  nucleus  of  the  human  ovum  there  are 
chromosomes.  The  ovum  is  formed  in  a 
special  organ,  the  ovary,  and  at  certain 
periods  the  ovum  is  extruded  into  the  Fallo- 
pian Tube,  a  duct  which  leads  to  the  uterine 
cavity. 

The  male  element,  the  spermatozoon,  is  a 
minute  body  consisting  of  a  head  and  a  long 
vibratile  tail.  The  total  length  is  about  1  /500 
of  an  inch,  while  the  head,  which  is  the  im- 
portant part,  is  about  1/10  of  the  length. 
The  head  represents  the  nucleus  of  a  cell  in 
which  the  spermatozoon  has  been  developed, 
and  it  contains  the  all-important  chromatm 
The  spermatozoa  are  formed  in  enormous  num- 
bers in  the  cells  of  a  special  organ,  the  testis. 


ORIGIN  AND   DEVELOPMENT      43 

16.  It  is  remarkable  that  both  the  ova  and 
the  spermatozoa  appear  in  the  same  part 
of  the  early  embryo,  a  layer  of  germinal 
matter,  which  is  cut  off,  at  an  early  period, 
from  the  matter  that  is  to  form  the  body  of 
the  individual,  whether  male  or  female.  The 
exact  origin  of  the  reproductive  elements  has 
not  been  clearly  established.  It  is  suggestive 
that  immature  ova  are  found  in  the  ovary  of 
a  female  long  before  birth.  There  they  lie 
dormant,  or  undergo  very  slow  changes  till 
puberty.  The  early  origin  of  spermatozoa 
has  not  been  clearly  established;  the  cells 
that  produce  them  are  not  active  till  the  begin- 
ning of  adolescence.  In  the  female  the 
extrusion  of  ova  continues  until  perhaps  fifty 
years  of  age,  but  the  production  of  sperma- 
tozoa by  the  male  may  last  through  a  long 
life.  Many  intricate  arrangements  for  the 
nutrition  and  support  of  both  are  found  in 
the  ovary  and  testis.  Of  themselves,  at  all 
events  in  the  higher  animals,  neither  male 
nor  female  element  alone  can  originate  a  new 
individual.  The  two  must  unite  and  blend 
together  This  is  fecundation.  Antecedent 


41     PRINCIPLES   OF   PHYSIOLOGY 

to  this  event,  however,  both  the  sperma- 
tozoid  and  the  ovum  undergo  remarkable 
changes,  which  have  been  studied  in  certain  of 
the  simpler  forms  of  animals,  but  while  for 
obvious  reasons  these  phenomena  cannot  be 
followed  in  a  human  being,  there  is  every  reason 
to  suppose  they  are  of  the  same  nature.  These 
phenomena  consists  essentially  of  various  forms 
of  cell  division,  by  which,  in  the  case  of  the 
spermatozoa,  these  bodies  are  increased  four- 
fold, while  in  that  of  the  ovum,  by  a  process 
of  splitting  and  separating  of  the  chromosomes 
in  the  nucleus  or  germinal  vesicle,  half  of  the 
chromosomes  are  extruded  and  are  practically 
lost.  Thus,  suppose  the  number  of  chromo- 
somes before  these  changes  to  be  twenty,  ten 
are  thrown  out  and  ten  are  retained.  Fecunda- 
tion then  occurs  by  the  blending  of  the  head 
of  the  spermatozoid  (containing  chromosomes 
from  the  male  parent)  with  the  germinal 
vesicle  of  the  ovum  (containing  chromosomes 
from  the  female).  It  would  appear  that  the 
number  of  chromosomes  in  the  fecundated 
ovum  is  now  doubled,  that  is  to  say,  in  the 
case  we  have  supposed,  the  number  is  again 


ORIGIN  AND   DEVELOPMENT      45 

twenty,  but  half  are  now  maternal  and  half 
are  paternal.  This  is  believed  to  be  the 
physical  basis  of  heredity,  as  it  is  assumed 
that  hereditary  characteristics  are  conveyed  by 
the  chromosomes.  This  statement  implies  that 
hereditary  matter  has  been  transmitted  not 
from  parents  only  but  from  grandparents  and 
possibly  from  individuals  of  many  previous 
generations. 

17.  The    fecundated    ovum    then    divides 
into  two,  each  of  the  two  into  four,  and  so  on 
until  a  large  number  of  cells  are  formed — and 
by  a  remarkable  series  of  processes,  known  as 
Karyokinesis,    each    cell,    when    it     divides, 
transmits  to  its  two  descendants  exactly  the 
same    number    of    chromosomes,    one    half 
representing  the  male  while  the  other  half 
represents  the  female  side.     Thus,  according  to 
modern  theory,  every  cell  in  the  body  may  possess 
hereditary  characteristics. 

18.  The  early  cells  form  certain  layers  from 
which  all  the  organs  and  tissues  of  the  body 
are  developed. 

The  early  embryonic  tissue  in  which  the 
future  being  is  formed  is  composed  of  two 


46     PRINCIPLES  OF  PHYSIOLOGY 

portions.  One  part  is  called  the  trophoblast. 
It  has  to  do  with  the  formation  of  structures 
for  connecting  the  ovum  with  the  mucous 
layer  of  the  uterus  in  which  the  embryo  is 
to  spend  the  first  part  of  its  existence.  The 
other  is  the  blastoderm,  in  which  the  future 
being  is  to  be  developed.  The  blastoderm 
divides  into  three  germinal  layers,  an  inner 
called  the  endoderm,  an  outer  named  the 
ectoderm,  and  between  the  two  a  third,  the 
mesoderm.  The  embryo  at  first  consists  of 
only  two  layers,  the  endo-  and  ecto-derm,  but 
at  a  very  early  period  the  mesoderm  makes  its 
appearance  and  is  probably  formed  by  the 
other  two.  In  turn,  the  mesoderm  splits 
into  two  layers,  one  of  which  becomes  closely 
adapted  to  the  ectoderm,  to  form  a  thick  layer, 
the  somatppleure,  while  the  other  clings  to  the 
endoderm  and  becomes  the  splanchnopleure. 
The  somatopleure  becomes  the  wall  of  the  body, 
and  the  splanchnopleure  forms  the  outer  wall 
of  the  alimentary  canal.  Between  the  two 
there  is  a  space,  the  body  cavity,  which,  in 
full  development,  constitutes  the  pleural  and 
peritoneal  cavities,  in  which  lie  the  viscera  of 


ORIGIN  AND  DEVELOPMENT      47 

the  body.  Several  layers  may  combine  in 
the  formation  of  the  various  organs  and 
tissues.  A  transverse  muscular  partition,  the 
diaphragm,  divides  the  body  cavity  into  two, 
the  thorax  and  the  abdomen, 

19.  From    the    ectoderm    are    derived    the 
epidermic  covering,  the   skin,  and  structures 
such  as  nails  and  hair  ;   the  epithelium  of  the 
glands  of  the  skin,  of  the  mammary  gland,  of 
the  anterior  part  of  the  mouth,  of  part  of 
the   alimentary   canal   at   the   anus,    of   the 
anterior   part    of   the   nasal    openings,  of   a 
portion  of  the  pituitary  body,  the  enamel  of 
the  teeth  ;  the  whole  of  the  nervous  system  ; 
the  epithelium  of   the  sense   organs,   and  a 
portion    of    the    suprarenal    bodies.      It    is 
important  to  observe  that  the  nervous  system 
and  the  sensory  layers  of  the  organs  of  special 
sense  are  formed  from  the  outer  layer  of  the 
embryo. 

20.  Passing  to  the  inner  layer,  the  endoderm, 
we  find  it  develops  into  the  epithelium  of  the 
alimentary  canal  and  the  glands  communicat- 
ing with  it ;  the  epithelium  of  the  two  Eusta- 
chian  tubes  passing  from  the  throat  to  the 


48     PRINCIPLES  OF  PHYSIOLOGY 

tympanum,  or  middle  ear  ;  the  lining  of  the 
tympanum  itself ;  the  epithelium  of  the 
respiratory  passages,  larynx,  trachea,  bronchi, 
and  pulmonary  air  cells  ;  the  epithelium  of 
the  thymus  and  thyroid  bodies ;  and  the 
epithelium  of  the  urinary  bladder  and  of  a 
portion  of  the  urethra. 

21.  From  the  epithelial  portion  of  the 
mesoderm,  that  is  the  somatopleure  portion 
of  the  mesoderm,  are  developed  all  the 
voluntary  muscles,  the  epithelium  of  the 
Wolffian  and  Mullerian  ducts  (primitive  excre- 
tory organs) ;  the  epithelium  of  the  excretory 
tubules  of  the  kidneys  and  Wolffian  bodies  ; 
the  epithelium  of  the  lining  of  the  body  cavity, 
sometimes  called  endothelium,  the  cortex  of 
the  suprarenal  body,  and  some  of  the  cells 
of  the  ovary  and  testis.  Possibly  the  germ 
cells  are  formed  in  this  layer,  but  their  place 
of  origin  has  not  been  conclusively  established. 
Lastly,  from  the  mesenchyme,  that  is  the 
splanchnopleure  layer  of  the  mesoderm  that 
has  become  associated  with  the  endoderm, 
we  find  developed  the  connective  tissues, 
involuntary  muscles,  the  spleen,  the  lymphatic 


ORIGIN  AND  DEVELOPMENT     49 

glands,  lymphoid  or  adenoid  tissue  in  various 
organs,  the  lining  epithelium  of  the  heart  and 
blood  and  lymph  vessels  (endothelium)  the 
red  corpuscles  of  the  blood,  and  probably,  but 
not  certainly,  the  white  corpuscles  of  the 
blood. 

22.  As  already  pointed  out,  the  portion  of  the 
ectoderm  that  takes  no  part  in  the  formation 
of  the  embryo  is  known  as  the  trophoblast. 
This  structure  by  and  by  comes  into  relation 
with  the  maternal  tissues  in  the  uterus  and 
an  important  organ  is  formed,  the  placenta. 
By  means  of  this  organ  the  blood  of  the  mother 
is  brought  into  close  relation  with  the  blood  of 
the  offspring.  A  thin  membrane  and  layers 
of  cells  intervene,  and  both  respiratory  and 
nutritional  changes  are  carried  on.  The  foetus 
breathes  by  the  placenta,  receiving  oxygen 
from  the  mother's  blood  and  giving  up  to  it 
carbonic  acid.  The  placenta  also  supplies 
materials  for  the  nourishment  of  the  foetus, 
and  no  doubt  proteins,  carbo-hydrates,  fats, 
saline  matters,  and  water  are  thus  supplied, 
for  the  growth  of  the  foetal  tissues.  At  this 
period  the  tissues  of  the  foetus  are  so  nourished 


50     PRINCIPLES   OF   PHYSIOLOGY 

as  to  ensure  constant  growth,  while  its  sluggish 
life  implies  the  production  of  a  minimum  of 
waste  products.  Thus  growth  goes  on  steadily 
and  with  astonishing  rapidity.  Tissue  after 
tissue  and  organ  after  organ  are  formed,  not  in 
a  definite  order  as  regards  time  but  contem- 
poraneously, as  if  some  kind  of  directive  agency 
were  at  work.  There  are  even  examples  of 
something  like  foreknowledge  in  the  building 
up  of  the  fcetus.  Stores  of  glycogen  are  sup- 
plied for  the  nutrition  of  embryonic  tissues. 
Iron  is  collected  in  the  body  of  the  foetus, 
from  the  mother's  blood,  so  that  an  abundance 
of  this  metal,  all  important  for  the  develop- 
ment of  red  blood  corpuscles,  is  found  in  the 
newly-born  when  in  the  new  condition  of  exist- 
ence it  is  nourished  by  milk,  which  contains 
only  a  small  supply  of  iron.  Iron  is  needed, 
but  as  the  milk  does  not  contain  enough  of  iron 
for  the  wants  of  the  organism  during  lactation, 
the  child  utilizes  the  iron  that  has  been  already 
stored.  In  development,  too,  one  of  the  most 
remarkable  phenomena  is  the  formation  of 
organs  in  most  of  which  tissues  take  part  that 
are  supplied  by  different  layers  of  the  embryo. 


ORIGIN   AND   DEVELOPMENT      51 

Thus,  as  an  example,  the  framework  of  the 
liver  is  formed  by  connective  tissue  from  the 
mesoderm,  while  the  hepatic  cells  are  derived 
from  the  cells  of  the  endoderm  and  have  the 
same  origin  as  the  cells  lining  the  alimentary 
canal.  To  bring  those  two  structures  together 
to  form  a  liver  implies  growth  from  different 
points  and  at  the  proper  time. 

23.  Each  tissue  and  organ  has  its  heredi- 
tary peculiarities.  These  are  often  obvious  in 
the  features,  the  colour  of  the  eyes  and  hair, 
and  the  stature  ;  they  are  seen  also  in  many  of 
those  mental  peculiarities  that  contribute  to 
the  making  of  character  and  individuality  ; 
but  they  are  not  so  evident  in  the  arrange- 
ments of  individual  organs.  There  can  be 
little  doubt,  however,  that  hereditary  char- 
acters may  affect  all  the  tissues  and  organs 
of  the  body.  They  are  not  merely  superficial. 
All  of  these  remarkable  phenomena  that  lie 
at  the  beginning  of  life  are  physiological 
processes  ;  but  science  has  not  yet  been  able 
to  trace  them  from  the  physiological  stand- 
point. Interest  in  them,  at  present,  is  mainly 
morphological,  that  is  as  regards  the  laws  that 


52     PRINCIPLES  OF  PHYSIOLOGY 

regulate  form  in  living  mechanisms,  but 
physiological  considerations  cannot  be  ex- 
cluded. How  are  we  to  explain  the  forces 
in  operation  in  producing  the  cleavages  and 
movements  that  are  apparent  ?  How  can  we 
account  for  the  nutrition  of  the  chromatin, 
said  to  be  the  fundamental  basis  of  heredity, 
by  which  it  multiplies  itself  ?  Is  there,  as 
some  suppose,  an  inner  world  of  molecular 
movement  in  the  chromatin,  by  which,  influ- 
enced by  nutrition  and  by  a  kind  of  struggle  for 
existence  and  survival  of  the  fittest,  new  com- 
binations of  chromatin-particles  are  effected  so 
as  ultimately  to  produce  individuals  different 
in  some  ways  from  their  parents,  or  are  the 
phenomena  only  under  the  laws  of  chance  like 
the  results  of  the  rattle  of  the  dice  box  ? 
These  are  all  profound  questions  lying  at  the 
very  basis  of  physiology. 

24.  Not  many  years  ago  it  was  not  uncom- 
mon for  physiologists  to  think  of  the  repro- 
ductive elements,  ova  and  spermatozoa,  as 
practically  structureless,  and  to  regard  them 
as  being  composed  simply  of  granular,  jelly-like 
matter.  Since  then,  owing  to  the  improve- 


ORIGIN  AND  DEVELOPMENT     53 

ments  in  microscopes  and  in  the  methods  of 
microscopy,  structure  has  been  rendered 
apparent  where  it  was  not  supposed  to  exist. 
Physicists  had  endeavoured  to  fix  physiolo- 
gists on  the  horns  of  a  dilemma.  Either  an 
ovum  must  have  structure,  which  physiologists 
at  one  time  doubted,  otherwise  complicated 
structures  must  have  been  evolved  out  of 
what  was  structureless  (which  is  inconceivable) 
or,  if  the  physiologists  admit  the  existence 
of  structure,  then  the  minute  cubical  capacity 
of  the  fecundated  ovum  could  not  contain  all 
the  organic  molecules  necessary  to  account 
for  the  transmission  of  hereditary  characteris- 
tics. Since  this  criticism  was  made,  in  the 
first  place,  structure  in  a  fecundated  ovum  has 
been  admitted,  and,  in  the  second,  we  now  have 
more  accurate  estimates  of  the  size  of  atoms 
and  molecules  than  was  then  available,  with 
the  result  that,  even  in  the  minute  cubical 
mass  of  a  fecundated  ovum,  there  is  room 
enough  for  all  the  molecules  necessary  to 
transmit,  by  their  combinations,  all  that  is 
required  to  account  for  even  minute  character- 
istics in  offspring.  Further,  the  new  physical 


54     PRINCIPLES   OF   PHYSIOLOGY 

conception  of  an  atom,  or  molecule  as  matter 
in  which  there  is  incessant  movement,  to 
and  fro  and  rotatory,  makes  it  still  less 
difficult  to  conceive  of  a  physical  basis  for 
heredity. 


CHAPTER    V 

DEVELOPMENT   OF  TISSUES   AND    ORGANS 

25.  WE  have  seen  that  the  first  organized 
matter  that  forms  the  physical  basis  of  life 
is  protoplasm.  Then  appears  the  more 
specialized  form,  the  cell,  and  from  the 
primitive  cells  the  layers  of  the  embryo  are 
developed.  From  these  layers  the  various 
organs  and  tissues  of  the  future  being  are 
produced.  All  embryonic  tissues  are  very 
similar  to  each  other,  consisting  of  protoplasm, 
in  which  appear  nuclei  and  cells  in  a  more  or 
less  rapid  state  of  transition.  From  these  the 
various  tissues  are  formed.  The  cells  cover- 
ing surfaces,  either  external,  or  those  lining  the 
alimentary  canal  and  the  ducts  and  pouches 
of  the  various  glands,  form  a  layer  termed 
epithelium.  Such  epithelial  cells  may  be 
close  together  to  form  a  single  layer,  or  the 

layer  may  consist  of  cells  three  or  four  deep, 
55 


56     PRINCIPLES   OF  PHYSIOLOGY 

in  different  degrees  of  development,  those  on 
the  surface  being  fully  formed.  It  is  to  be 
noted  that  all  free  surfaces  are  covered  by 
such  cells,  and  it  follows  that  matter 
can  neither  enter  the  tissues  of  the  body, 
nor  issue  from  them  into  the  external  world, 
without  passing  through  an  epithelial  layer. 
Such  matters  do  not,  however,  pass  through 
epithelium  as  a  fluid  passes  through  a  filter, 
but  the  matter  is  modified  chemically  and 
physically  by  the  epithelial  cells. 

26.  Other  cells  become  differentiated  into 
tissues  that  form,  as  it  were,  the  framework 
of  the  body,  moulding  the  shape  of  organs,  and 
supporting  their  constituent  structures.  These 
are  called  the  connective  tissues.  This  variety 
of  tissue  is  so  abundant  as  to  exist  in  every 
organ,  while  it  forms  a  framework  for  every 
other  tissue.  Sometimes  it  is  soft  and  con- 
sists of  delicate  fibres  forming  networks  or 
membranes  or  cords  (as  in  sinews),  but  it  may 
be  infiltrated  with  earthy  matter,  and  form 
a  hard  structure  of  bone,  and  again  it  may  be 
hard,  without  earthy  matter,  in  cartilage  or 
gristle.  Lying  in  it,  we  always  find  cells  in  a 


TISSUES  AND  ORGANS  57 

condition  of  vital  activity,  and  these  cells 
produce  the  intervening  substance,  such  as  the 
fibres  of  ordinary  connective  tissue,  the  solid 
basis  of  gristle  or  the  hard  substance  of  bone. 
All  such  cells  are  engaged  in  forming  a  frame- 
work to  support  other  structures,  and  they 
can  also  repair  any  injury  to  an  organ,  such 
as  may  be  caused  by  a  cutting  instrument. 
Thus,  a  wound  of  the  skin  is  healed  and  filled 
up  by  connective  tissues,  as  seen  in  a  cicatrix 
or  scar.  So  abundant  is  connective  tissue 
that  if  we  can  imagine  the  body  to  be 
immersed  in  a  fluid  which  dissolved  all  the 
tissues  except  connective  tissues,  we  should 
still  have  a  cast  of  the  body,  spongy-like 
in  structure,  formed  of  this  tissue.  It  is 
richly  supplied  with  blood  by  fine  capillaries 
and  by  numerous  lymphatic  spaces  and 
channels  for  drainage  of  lymph.  No  doubt 
it  is  the  scene  of  active  physiological  changes. 
27.  The  next  tissue  of  importance  is  mus- 
cular or  contractile  tissue,  of  which  there  are 
several  varieties.  The  masses  of  flesh  we 
find  on  the  trunk  and  limbs  are  composed  of  a 
variety  of  this  tissue  called  striated  muscle, 


58     PRINCIPLES  OF   PHYSIOLOGY 

on  account  of  its  striped  appearance  when 
examined  microscopically.  It  consists  of  a 
mass  of  elongated  nucleated  cells,  each  an 
inch  or  two  in  length,  having  pointed  ends,  and 
its  minute  structure  is  so  complicated  that  it 
is  still  one  of  the  puzzles  of  histologists.  The 
cell  substance  has  become  highly  differentiated 
into  disk-like  structures,  which  give  the 
tissue  an  appearance  of  striation,  that  is  of 
bands  passing  transversely  across  the  fibre. 
There  is  also  a  differentiation  into  longitudinal 
structures  called  sarcostyles  or  fibrils,  each  of 
which  shows  striation,  due  to  the  existence 
of  sarcous  elements,  or  sarcomeres.  When  a 
fibre  contracts  the  sarcous  elements  contract 
and  a  fluid  substance,  the  sarcoplasm,  is 
pressed  out  in  both  directions  till  it  is  arrested 
by  a  thin  membrane,  the  membrane  of  Krause. 
This  membrane  passes  transversely  across  a 
fibre  and  separates  bundles  of  sarcostyles. 
The  sarcous  elements  are  doubly  refractive, 
while  the  other  parts  between  are  singly 
refractive.  There  appears  also  to  be  a  very 
fine  reticulum,  with  longitudinal  meshes, 
n  the  fibre  Another  variety,  called  non- 


TISSUES   AND   ORGANS  59 

striated  muscle,  consists  of  elongated  cells, 
with  no  striation.  It  is  found  chiefly  in  the 
wall  of  the  stomach  and  bowel,  in  the  ducts  of 
glands,  in  the  walls  of  blood  vessels,  and  in 
the  skin. 

Finally,  we  find  the  power  of  movement, 
or  contractility,  manifested  by  many  cells, 
usually  isolated  in  a  fluid,  or  embedded  in  a 
tissue.  Thus  the  white  blood  corpuscles 
(leucocytes  of  several  varieties),  cartilage 
cells,  the  cells  in  bone,  connective  tissue  cells, 
the  cilia  (hair-like  structures)  found  on  some 
epithelial  cells,  are  all  contractile  and  are 
capable  of  changing  their  shape.  All  forms 
of  contractile  tissues  are  for  purposes  of 
movement.  Thus  the  movements  of  the 
limbs  in  locomotion,  and  the  movements  of 
the  chest  Avail  in  respiration,  are  effected 
by  means  of  striated  muscles.  Again,  the 
slow  contractions  by  which,  during  diges- 
tion and  absorption,  the  food  stuffs  are 
propelled  along  the  alimentary  canal,  are 
effected  by  non-striated  muscle.  The  heart 
beats,  the  changes  in  the  calibre  of  the 
smaller  arteries  by  which  the  quantity  of 


60     PRINCIPLES  OF   PHYSIOLOGY 

blood  going  to  a  part  is  regulated,  movements 
in  certain  ducts,  as  in  the  ureter  (the  duct 
passing  from  the  kidney  to  the  bladder),  the 
contractions  of  the  skin,  are  all  effected  by 
non-striated  muscle.  The  contractions  of 
cilia  create  a  current  in  one  direction,  as  in 
those  in  the  respiratory  passages  causing  a 
movement  of  air  and  mucus  towards  the 
opening  of  the  respiratory  passage.  The 
leucocytes,  by  their  contractions,  can  pass 
out  of  the  vessels  into  surrounding  tissues, 
and  there  they  may  seize  hold  of,  kill,  and 
digest  foreign  organisms,  such  as  many  bacteria 
and  bacilli  that  cause  disease.  Probably,  also, 
by  this  power  of  ingesting  foreign  bodies, 
they  take  part  in  processes  of  nutrition.  All 
contractile  tissues,  except  the  isolated  cells, 
are  related  to  the  central  nervous  system  by 
nerves  that  pass  to  and  from  these  centres 
to  the  contractile  tissues.  They  are  also 
very  richly  supplied  with  blood  vessels,  and 
they  are  nourished  by  the  fluid  that  passes 
out  of  the  vessels,  and  bathes  every  fibre. 
This  fluid,  called  lymph,  carries  away  all 
excess  of  fluid,  and  also  many  substances  in 


TISSUES  AND  ORGANS  61 

solution  that  are  formed  by  the  destruction  of 
muscle  substance,  or  of  chemical  matters 
in  it,  during  contractile  activity.  Contractile 
tissue  constantly  requires  oxygen,  and  it 
constantly  produces  carbonic  acid ;  this  is 
so,  even  during  the  resting  of  muscle,  but, 
when  it  contracts,  much  more  oxygen  is  used 
and  much  more  carbonic  acid  is  produced. 
So  complicated  are  the  chemical  processes 
in  contractile  tissue  that  there  is  still  uncer- 
tainty regarding  them. 

28.  The  controlling  and  regulating  tissue  is 
nervous  tissue.  It  is  found  in  the  brain, 
spinal  marrow,  ganglia,  parts  of  the  organs 
of  sense,  and  in  nerves,  and  it  consists  of 
nerve  fibres  and  nerve  cells.  These  will  be 
more  fully  considered  when  we  treat  of 
nervous  actions.  Suffice  it  to  say  here 
that  nerve  fibres  generate  and  conduct  what 
we  term  a  nervous  impulse,  a  change,  the 
true  nature  of  which  we  do  not  know. 
Such  an  impulse,  issuing  from  a  nerve 
centre,  such  as  a  portion  of  the  spinal 
cord,  may  travel  to  a  muscle  and  cause  the 
striated  tissue  to  shorten,  when  there  may 


62     PRINCIPLES   OF   PHYSIOLOGY 

be  movement  of  a  limb ;  or  it  may,  when 
it  reaches  the  non-striated  muscle  in  the 
bowel,  cause  slow  ring-like  movements  of 
the  tube  (peristaltic) ;  or  it  may  affect  the 
number  and  strength  of  the  heart  beats,  or  it 
may  cause  the  walls  of  small  arteries  to  con- 
tract and  thus  regulate  the  amount  of  blood 
flowing  through  them  ;  or  it  may  stimulate 
the  activity  of  a  secretion,  as  seen,  for  example, 
in  the  increased  flow  of  saliva  when  a  sapid 
substance  is  in  the  mouth,  or  even  when 
the  sight  or  thought  of  delicious  food  has 
the  same  effect.  The  electric  discharge  of  an 
electric  fish  is  also  under  the  control  of  the 
nervous  system,  which  also  appears  to  affect 
the  light  of  the  firefly,  glowworm,  and  even 
the  light  of  the  luminous  organs  found  in  some 
fishes  that  live  in  the  profound  darkness  of 
the  depths  of  the  ocean.  Finally,  in  the  nerve 
cells  that  form  the  main  part  of  the  nerve 
centres,  such  as  the  brain  and  spinal  cord, 
there  are  molecular  changes  of  which  we  know 
next  to  nothing,  and  yet  on  these  all  nervous 
activities  depend,  even  those  associated  with 
mental  processes. 


TISSUES   AND   ORGANS  63 

29.  It  would  seem  that  during  countless 
ages  evolution  has  slowly  built  up  a  great 
variety  of  animals.  This  evolutionary  process 
has  also  affected  more  or  less  every  tissue. 
We  may  detect  primitive  types  of  tissue,  such 
as  we  find  in  the  embryo,  in  the  tissue  of  the 
placenta  and  umbilical  cord,  in  the  cells 
between  the  bodies  of  the  vertebrae,  in  the 
vitreous  humour  of  the  eye,  in  the  so-called 
lymphoid  tissue  found  in  various  organs, 
and  in  connective  tissues  generally.  Cartilage 
or  gristle  has  preceded  bone.  Non-striated 
may  be  regarded  as  more  primitive  than 
striated  muscle.  Even  some  striated  muscles 
seem  to  be  more  primitive  than  others.  These 
muscles  are  usually  pale,  but  certain  muscles, 
such  as  the  semi-membranous  muscle  in  a 
rabbit's  leg,  are  red.  Red  muscles  contract 
more  slowly  than  pale  muscles,  and  their 
structure  seems  to  be  of  a  lower  type.  Nervous 
tissues  have  passed  through  many  forms,  until 
we  reach  the  highly  complicated  cells  of  the 
nerve  centres.  The  nervous  elements  of  the 
sense  organs  also  show  differentiation  as  we 
pass  from  lower  to  higher  forms.  Thus  the 


64     PRINCIPLES   OF  PHYSIOLOGY 

retinal  elements  of  the  eye  of  a  codfish  are 
very  different  from  those  in  the  human  retina. 
Little  attention  has  yet  been  paid  to  the 
evolution  of  tissues,  and  the  question  of 
whether  it  has  been  brought  about  by  the 
agency  of  external  circumstances  on  a  particu- 
lar tissue,  or  by  the  influence  of  one  tissue  on 
another,  cannot  yet  be  answered.  It  is  strik- 
ing, however,  to  observe  that  evolution,  which 
depends  on  physiological  processes,  affects  not 
merely  the  outward  form  but  even  the  tissues 
that  build  up  the  body  of  an  animal. 


CHAPTER    VI 

MATTER    AND    ENERGY   IN   THE    LIVING 
BODY 

30.  Matter  and  chemical  processes.  As  has 
already  been  pointed  out,  the  phenomena  of 
life  depend  on  chemical  changes  occurring  in 
the  body.  These  changes  are  largely  oxida- 
tions, that  is  the  union  of  oxygen  with  cer- 
tain constituents  of  the  body,  and  decomposi- 
tions, that  is  the  splitting  up  of  more  complex 
chemical  substances  into  simpler  ones.  There 
are  also,  to  some  extent,  reductions,  that  is, 
the  taking  of  oxygen  from  chemical  constitu- 
ents ;  and  there  are  syntheses,  the  reverse  of 
decompositions,  or  the  building  up  of  com- 
plex substances  from  simpler  ones. 

81.  We  are  still  ignorant  of  the  exact 
nature  of  many  of  the  chemical  processes 
occurring  in  living  tissue,  but  they  may  be 
shortly  noticed. 

B  65 


66     PRINCIPLES   OF   PHYSIOLOGY 

(1)  Oxidation  is  the  most  common  chemical 
reaction.  By  continuous  processes  of  oxida- 
tion complex  bodies  are  split  up  into  simpler 
ones.  Thus  by  oxidation,  protein,  such  as 
exists  in  white  of  egg,  may  be  split  up  into 
leucin,  tyrosin,  glycine,  and  the  fatty  acids  ; 
uric  acid  into  urea,  allantoin,  oxalic  acid  and 
carbonic  acid.  Oxidation  has  been  carried 
out  by  the  chemist,  with  the  production  of 
chemical  substances  the  same  as  those  found 
in  the  fluids  and  tissues  ;  and  the  inference 
is  that  in  the  living  body  they  are  also  pro- 
duced by  oxidation.  But  in  living  matter 
the  processes  are  obscure,  and  there  are 
probably  intermediate  steps  still  unknown. 
There  can  be  little  doubt  that  oxidations 
occur  almost  wholly  in  the  tissues ;  but 
we  must  avoid  taking  too  mechanical  a 
view  of  the  nature  of  oxidation  in  living 
matter.  There  is  no  such  phenomenon  as 
the  direct  union  of  oxygen  with  carbon,  or 
with  hydrogen,  as  in  burning  a  candle.  The 
combustion  of  a  candle  will  always  yield,  for  a 
given  weight,  the  same  amount  of  carbonic 
acid  and  of  water,  and  the  same  amount  of 


MATTER   AND   ENERGY  67 

oxygen  will  be  used  up.  But  there  is  no 
parallelism  in  the  so-called  oxidation  in  living 
stuff.  Oxygen  may  disappear  in  the  process, 
and  the  amount  of  combustion  products  cannot 
always  be  accounted  for  by  the  amount  of 
oxygen  used.  Oxidation  in  living  matter  is 
a  complicated  process. 

(2)  Reduction  is  due  to  the  abstraction  of 
oxygen.     It  plays  an  important  part  in  the 
chemistry  of  plant  life,  but  it  is  not  so  common 
in  the  animal  body.     Fats  may  be  formed 
from    carbo-hydrates,    as    in   the   feeding   of 
pigs  with  starchy  matter ;    much  more  fat  is 
formed  than  can  be  accounted  for  by  the  fat 
in  the  food.     But  fats  presumably  are  formed 
from   carbo-hydrates   (starches,  sugars,  etc.), 
by  the  abstraction  of  oxygen.     Not  a   few 
substances   passed   through  the  body   suffer 
reduction.     Thus   the  iodides   and  bromides 
of  the  alkalies  are  formed  from  iodates  and 
bromates,  and  malic  acid  (as  in  fruits),  becomes 
succinic  acid. 

(3)  Decompositions  frequently  occur,  when 
complex    substances    are    split    into    simpler 
ones.     Thus  taurocholic  acid,  the  acid  of  one 


68     PRINCIPLES   OF   PHYSIOLOGY 

of  the  salts  found  in  bile,  taurocholate  of  soda, 
may  be  resolved  into  its  two  constituents, 
taurine  and  cholalie  acid.  Sometimes  water 
is  removed  from  a  compound,  and  the  remain- 
der then  decomposes.  Thus  creatin,  a  sub- 
stance found  in  flesh- juice,  by  the  abstraction 
of  water  becomes  creatinin,  which  is  voided 
in  the  urine.  On  the  other  hand  there  is  a 
reverse  process.  Water  may  be  first  taken  up  in 
chemical  combination,  and  a  new  substance 
then  formed.  Thus  urea,  found  in  the 
urine,  combines  with  water,  and  there  is  then 
a  re-formation  of  the  molecules  to  form  car- 
bonate of  ammonia. 

(4)  Living  matter,  in  certain  circumstances, 
may  combine  with  oxygen,  and  possibly  with 
other  bodies,  not  by  a  chemical  combination, 
but  by  a  physical  process  depending  on  tem- 
perature and  pressure.  This  has  not  been 
absolutely  proved  with  protoplasm,  but  it 
is  suspected.  The  colouring  matter  of  the 
red  blood  corpuscle,  a  highly  complex  sub- 
stance called  haemoglobin,  combines  with 
oxygen  to  form  a  compound  known  as  oxy- 
haemoglobin.  The  amount  of  oxygen  taken 


MATTER  AND  ENERGY  69 

up  varies  directly  as  the  pressure  and  inverse- 
ly as  the  temperature.  Thus,  at  the  same 
temperature,  by  lowering  the  pressure  by 
placing  the  oxy-haemoglobin  in  the  partial 
vacuum  of  an  air  pump,  the  compound 
gives  off  the  oxygen,  without  itself  suffering 
decomposition.  When  the  pressure  is  raised, 
the  oxy-haemoglobin  again  takes  up  oxygen. 
This  process,  known  as  dissociation,  depends 
on  physical  conditions.  It  plays  an  important 
part  in  respiration. 

(5)  By  synthesis  is  meant  the  building  up 
of  complex  chemical  substances  by  the  union 
of  simpler  bodies.  This  has  been  accomplished 
by  the  chemist,  and,  as  already  stated, 
numerous  organic  bodies  have  been  formed 
artificially  in  the  laboratory,  such  are  urea, 
hippuric  acid,  glycine,  taurin,  creatin,  glu- 
cose, and  numerous  organic  acids,  such  as 
oxalic,  lactic,  succinic,  benzoic,  propionic, 
acetic,  and  formic  acids.  Even  bodies 
resembling  proteins  have  recently  been 
formed  synthetically,  and  it  is  probable 
that,  by  following  out  synthetic  processes 
that  are  suggested  by  theory,  proteins  of 


70     PRINCIPLES   OF   PHYSIOLOGY 

higher  complexity  may  yet  be  formed.  It 
is  not  easy  to  give  examples  of  syntheses  in  the 
animal  body.  If  benzoic  acid  is  given  in 
food  or  as  a  drug,  it  unites  with  glycine, 
probably  in  the  liver,  to  form  hippuric  acid, 
with  the  elimination  of  a  molecule  of  water 
Many  organic  acids  may  thus  be  built  up. 
Thus  aromatic  bodies  unite  with  sulphuric 
acid,  and  conjugated  sulpho-acids  thus  formed 
are  eliminated  by  the  kidneys.  No  doubt 
synthetic  processes  may  also  build  up  fatty 
phosphorized  substances  existing  in  nervous 
matter,  haemoglobin  (the  colouring  matter  of 
the  red  corpuscles),  and  even  proteins. 

(C)  Enzyme  or  Ferment  Action.  One  of  the 
most  interesting  chapters  in  the  history  of 
scientific  discovery  has  been  that  of  the 
nature  of  fermentation.  Fermentation  and 
putrefaction  have  been  known  from  early  times, 
but  their  true  nature  has  been  discovered  only  in 
comparatively  recent  years.  It  is  now  known 
that  both  are  connected  with  the  life-history 
of  micro-organisms,  such  as  in  the  ordinary 
fermentation  of  sugar  into  alcohol,  carbonic 
acid,  and  other  substances,  by  the  agency  of 


MATTER   AND   ENERGY  71 

various  kinds  of  yeast  cells  or  toruiae,  and  the 
putrefaction  of  dead  nitrogenous  matter  by 
the  activity  of  various  bacteria.  A  recogni- 
tion of  these  facts,  and  of  the  part  played  by 
micro-organisms  in  many  diseases,  has  led  to 
the  evolution  of  the  vast  realm  of  knowledge 
now  known  as  bacteriology.  Physiologists 
have  long  been  acquainted  with  the  existence 
in  the  body  of  ferments,  such  as  the  ptyalin 
of  the  saliva  and  the  pepsin  of  the  gastric 
juice,  but  it  is  only  in  recent  years  that  there 
has  been  an  adequate  recognition  of  the  part 
played  by  ferments  in  many  physiological 
processes.  It  is  now  known  that  all  ferments, 
or  enzymes,  as  they  are  now  called,  are  formed 
in  the  interior  of  cells.  For  a  long  time  it  was 
held  that  the  plant  known  as  the  yeast  cell 
effected  fermentation  in  the  juice  of  the  grape 
or  in  a  solution  of  sugar  by  its  vital  activity, 
and  this  view  was  favoured  by  the  fact  that 
durng  fermentation  there  was  a  remarkable 
multiplication  of  the  cells  of  the  yeast 
It  is  now  known,  however,  that  even  this 
fermentation  is  caused  by  an  enzyme  (zymase) 
formed  in  the  interior  of  the  yeast  cell. 


72     PRINCIPLES   OF   PHYSIOLOGY 

In  a  similar  way  all  enzymes  are  formed  in 
cells,  as,  for  example,  ptyalin  in  certain  cells 
of  the  salivary  glands,  and  pepsin  in  certain 
cells  in  the  tubular  glands  in  the  mucous 
membrane  lining  the  stomach. 

32.  The  enzyme,  however,  is  preceded  in 
the  cell  by  an  enzyme-forming  substance,  a 
zymogen,  as  it  is  called,  and  while  the  cell  is 
secreting,  matter  appears  in  the  form  of  small 
granules.  Thus  ptyalin  is  preceded  by  pty- 
alinogen,  pepsin  by  pepsinogen,  and  so  on. 
It  would  appear  that  just  when  the  secretion 
is  poured  out  the  zymogen  is  changed  into 
the  enzyme,  and  the  enzyme  at  once  begins 
to  act.  Each  enzyme  has  a  limited  field  of 
activity.  Thus  three  are  required  to  modify 
the  three  varieties  of  di-saccharides,  cane 
sugar,  milk  sugar  (lactose)  and  maltose,  one 
and  only  one  for  each  sugar.  The  activity  of 
enzyme  is  greatest  at  about  40°  C  :  at  about 
50°  C.  the  ferment  is  destroyed  Extreme 
cold  arrests  the  activity,  but  it  does  not  appear 
to  injure  it,  as  it  will  again  act  at,  say,  40°  C. 
One  remarkable  feature  of  the  action  of  an 
enzyme  is  that  only  a  small  amount  is  neces- 


MATTER  AND  ENERGY  73 

sary,  and  at  the  end  of  the  process  the  amount 
of  enzyme  is  the  same  as  at  the  beginning 
If  the  enzyme  is  used  up,  or  if  a  portion 
of  it  is  used  up,  there  must  be  a  process 
by  which  the  enzyme  is  reconstructed.  To 
avoid  this  difficulty,  it  has  been  supposed  that 
the  enzyme  acts  catalytically,  that  is,  merely 
by  its  presence.  It  is  difficult  to  imagine  that 
any  substance  can  modify  a  chemical  product 
merely  by  its  presence.  This  idea  arose  from 
the  fact  that  the  enzyme  appeared  to  be 
unaltered  in  the  process.  The  chemist  is  also 
aware  of  chemical  processes  influenced  by  the 
presence  of  inorganic  substances.  Thus  a 
mixture  of  oxygen  and  hydrogen  immediately 
explodes  when  brought  into  contact  with 
platinum  black.  If  so,  we  may  imagine  that 
some  kind  of  vibratory  action  is  communi- 
cated to  the  molecules  of  the  fermentable 
matter  from  the  enzyme,  and  that  this  vibra- 
tion causes  the  change  in  the  substance.  The 
analogy  is  that  of  sympathetic  vibrations 
between  two  tuning  forks  of  the  same  pitch. 
Thus  a  fork  Ut4  will,  if  caused  to  vibrate 
by  bowing,  at  once  set  in  action  the  prongs  of 


74     PRINCIPLES   OF   PHYSIOLOGY 

another  fork,  also  Ut4,  even  if  the  two  forks 
are  at  a  considerable  distance  from  each 
other  As  we  know  nothing  of  the  chemical 
constitution  of  enzymes,  except  that  they 
are  proteins,  this  can  only  be  a  conjecture, 
but  it  is  to  be  borne  in  mind  that  proteins  are 
very  unstable.  Enzymes  may  act  alone  or 
they  may  apparently  be  stimulated  by  other 
enzymes  or  by  the  presence  of  other  sub- 
stances. In  chemical  reactions  we  have  to 
consider  the  element  of  time,  or  what  we  may 
term  the  velocity  of  the  reaction.  It  would 
appear  that  all  so-called  catalytic  actions, 
including  the  action  of  enzymes,  have  the 
effect  of  quickening  the  velocity  of  the  chemi- 
cal changes  involved. 

33.  As  already  pointed  out,  enzymes  are 
formed  in  cells.  Cells  may  be  frozen  and  then 
pounded  into  a  paste.  Enzymes  are  thus  set 
free,  and  at  the  proper  temperature  they  will 
manifest  their  usual  activities.  This  shows 
that  they  do  not  depend  on  the  life  of  the 
cells.  There  can  be  no  doubt  that  as  almost 
all  cells  contain  enzymes,  they  take  part  in 
nutritional  processes,  by  exciting  changes  in 


MATTER  AND   ENERGY  75 

the  protoplasm  of  the  cell,  or  possibly  in  the 
substances  stored  in  the  cell.  They  may  thus 
carry  on  metabolic  changes,  during  the  life  of 
the  cell,  and  they  may  even  cause  destruction 
of  the  cell  after  death,  by  a  kind  of  auto- 
digestion,  or  autolysis. 

34.  Most  enzymes  are  hydrolytic,  that  is 
to  say,  we  may  represent  their  action  by  the 
addition  of  water  to  the  fermentable  matter 
and  then  a  decomposition.     Thus  cane  sugar 
plus  water  plus  the  enzyme,  is  changed  into 
dextrose  and  levulose,  two  other  varieties  of 
sugar.     But  other  enzymes  are  believed  to 
carry    oxygen   to    the  tissues.     These    have 
probably   to   do  with   respiratory   processes. 
They  are  termed  oxidases. 

35.  Enzymes    may    be    readily    classified 
thus  : — 

(1)  Amylolytic — Change      polysaccharides 
such  as  starch  into  sugar.     Example :  Ptyalin 
of  saliva  and  the  diastase  of  plants. 

(2)  Invertins — Change    disaccharides    into 
mono-saccharides.    Ex. :  Invertase  of  intestinal 
juice,  which  changes  cane  sugar  into  dextrose 
and  levulose. 


76     PRINCIPLES  OF  PHYSIOLOGY 

(3)  Steatolytic  or  Lipolytic — Decompose  fats 
into  fatty  acids  and  glycerine.     Ex. :  Steapsin 
or  Lipase  of  pancreatic  juice. 

(4)  Proteolytic — Change  proteins  into   pro- 
teoses,  peptones,  polypeptides,  and  at  last  into 
amino-acids.     Ex. :    Pepsin  of  gastric  juice  ; 
trypsin  of  pancreatic  juice. 

(5)  Peptolytic — Decompose     proteoses    and 
peptones  into  polypeptides  and  amino-acids. 
Ex.  :  Erepsin  of  intestinal  juice. 

(6)  Blood  ferments — Cause  clotting  of  blood. 
Ex. :    Thromhin  (fibrin  ferment) ;    rennin  of 
gastric  juice  converts  caseinogen  of  milk  into 
casein. 

(7)  Ferment  of  ferments — Enzyme  that  stim- 
ulates the  formation  and  action  of  the  trypsin 
of  the  pancreatic  juice.     Ex  :    Enterokinase  of 
duodenum. 

(8)  The   acid   chyme,  when   it   leaves   the 
stomach,  leads  to  the  formation  of  an  enzyme, 
secretin,  which  is  absorbed  into  the  blood  and 
stimulates  the  secretion  of  pancreatic  juice, 
Probably  other  chemical   substances  act  in 
a  similar  way,  on  various  secretions.     These 
are  called  hormones 


MATTER   AND   ENERGY  77 

36.  Matter  and  Energy.  All  chemical 
phenomena  are  associated  with  changes  in 
energy,  one  of  the  great  conceptions  of  modern 
physical  science.  Energy  may  be  latent  or 
locked  up  in  a  chemical  substance,  and  it  is 
then  said  to  be  potential.  Thus,  take  any  oil 
as  an  example.  An  oil  contains  carbon, 
hydrogen  and  oxygen  so  united  as  to  form  a 
complex  substance,  say  the  olein  of  olive  oil, 
each  molecule  of  which  has  a  definite  chemical 
composition.  The  oil  (or  the  olein),  however, 
is  conceived  to  be  associated  with  energy  in 
a  latent  state,  that  is  to  say,  the  energy  that 
binds  the  atoms  into  its  molecule  is  there 
locked  up,  and  so  long  as  it  is  so,  the  molecule 
is  chemically  inert.  But  if  it  be  oxidized,  that  is 
if  it  be  burned  in  a  suitable  contrivance,  say  a 
lamp,  the  oxygen  of  the  air  unites  with  the 
carbon  of  the  oil  to  form  carbonic  acid,  and 
with  the  hydrogen,  to  form  steam  or  water. 
The  carbon  appears  in  the  form  of  soot. 
But  during  the  burning,  energy  appears  as 
heat,  and  the  heat,  by  a  suitable  machine, 
might  be  converted  into  motion,  and  do 
work  by  lifting  a  weight  and  overcoming  the 


78     PRINCIPLES   OF   PHYSIOLOGY 

friction  of  a  train  of  wheels.  While  the  energy 
is  thus  doing  work  it  is  said  to  be  actual  or 
kinetic.  The  complete  combustion  of  a 
given  amount  of  olein  would  produce  a  certain 
equivalent  of  heat,  and  the  heat,  again,  might 
be  transformed  into  a  certain  equivalent  of 
motion.  There  is  a  fixed  quantitative  rela- 
tion between  the  two  modes  of  energy.  Thus 
physical  science  tells  us  that  a  unit  of  heat  is 
the  amount  of  heat  that  is  required  to  raise 
the  temperature  of  1  gramme  (15.4324  grains) 
from  15°  to  16°  centigrade,  and  the  unit  of 
work  is  the  grammetre,  or  the  amount  of  work 
expended  in  lifting  1  gramme  to  the  height  of  1 
metre  (39.37  inches).  Apply  this  to  a  special 
case ;  a  decomposition  liberating  heat,  develops 
1  heat  unit,  and  this  heat,  if  it  does  mechanical 
work,  will  perform  424  grammetres  of  work. 
Thus  1  unit  of  work  may  be  converted  into 
1  unit  of  heat,  and  conversely. 

37.  Energy  therefore  may  be  either  potential 
or  kinetic.  When  simple  substances  are 
combined  to  form  complex  ones,  energy 
becomes  latent  or  potential,  and  when  a 
complex  substance  is  split  up  into  simpler 


MATTER  AND  ENERGY  79 

ones  energy  becomes  kinetic;  it  may  appear, 
for  example,  as  heat  or  motion.  In  the  case 
we  are  considering,  it  is  possible  to  determine 
with  accuracy  the  energy  the  oil  contains,  or, 
in  other  words,  the  heat  produced  by  its 
combustion  ;  this  amount  of  heat  is  conceived 
as  kinetic  energy  ;  and  if  it  were  possible,  by 
a  synthetic  process,  so  to  combine  the  carbon, 
hydrogen,  and  oxygen  as  to  re-form  the  olein, 
the  same  amount  of  energy  would  have  to  be 
expended  as  was  liberated  by  decomposition. 
In  any  such  system  of  operations  the  sum  of 
the  energy  at  the  close  would  be  the  same  as 
at  the  beginning. 

38.  Chemical  Substances.  We  are  now  in 
a  position  to  consider  from  the  chemical 
point  of  view,  the  matter  of  which  the  body  is 
composed.  The  chemical  elements  in  living 
matter  have  been  referred  to  in  section  7. 
These  elements  are  combined  to  form  chemi- 
cal compounds,  divided  into  organic  and 
inorganic.  Organic  compounds  are  again 
classified  into  nitrogenous  and  non-nitrogen- 
ous. The  nitrogenous  are  the  more  important ; 
they  are  necessary  for  the  constitution  of 


80     PRINCIPLES   OF   PHYSIOLOGY 

protoplasm.  It  must  be  observed  that  a 
chemical  analysis  of  living  matter  is  not 
possible,  because,  in  the  processes  to  which  it 
must  be  subjected,  the  condition  we  associate 
with  life  disappears.  The  living  matter  is 
killed  by  the  attempt  at  analysis,  so  that  what 
we  are  able  to  analyse  is  dead  matter  that 
was  once  alive.  Suppose  a  chemist  is  asked  to 
reveal  to  us  the  chemical  constituents  of  a 
muscle,  he  might  be  able  to  enumerate  the 
elements  of  which  it  was  composed.  This 
would  teach  us  very  little.  But  during  the 
analysis  it  would  be  found  that  numerous 
more  or  less  complicated  chemical  substances 
appeared,  and  that  these  could  be  arranged 
into  groups,  the  members  of  which  showed 
certain  characters  in  common.  In  this 
way  we  learn  that  organic  matter  is  built 
up  of  certain  compounds  called  proximate 
constituents,  or  principles,  already  referred  to 
These  are  proteins,  carbo-hydrates,  and  fats, 
and  along  with  these  we  find  many  other 
substances  which  are  derivatives  of  these  three, 
along  with  various  saline  substances  and  water. 
39.  The  proteins  are  bodies  of  highly 


MATTER   AND   ENERGY  81 

complex  chemical  constitution.  They  all 
contain  about  16  per  cent,  of  nitrogen,  along 
with  carbon  (more  than  half  their  weight), 
hydrogen,  oxygen,  and  usually  a  small  amount 
of  sulphur  or  phosphorus,  or  both.  Proteins, 
a  typical  example  of  which  we  find  in  the 
albumen  in  white  of  egg,  are  essential  in 
protoplasm,  and  they  are  more  intimately 
associated  with  the  phenomena  of  life  than 
any  of  the  other  proximate  principles,  in  the 
sense  that  wre  never  find  vital  phenomena 
without  them,  and  that  vital  phenomena  are 
never  manifested  by  carbo-hydrates,  fats,  saline 
matter,  or  water,  either  alone  or  in  combination. 
Proteins  are  usually  colloidal  or  glue-like,  and 
are  non-diffusible  through  animal  membranes. 
A  colloid  does  not  form  a  true  solution,  but  in  a 
fluid  it  forms  a  kind  of  emulsion  consisting  of 
minute  particles  or  globules  suspended  in  the 
fluid.  (Such  an  emulsion- colloid  is  termed 
a  gel,  but  there  are  colloids,  having  much 
finer  particles,  and  which  have  different 
properties.  Such  are  called  sols.  Proto- 
plasm, alive,  is  probably  of  the  nature  of  a 
sol.) 


82     PRINCIPLES  OF  PHYSIOLOGY 

Of  the  true  chemical  structure  of  proteins 
we  know  little,  but  it  has  been  shown  that 
by  various  agencies  they  split  up  into  numer- 
ous simpler  bodies  which  also  may  be  arranged 
in  groups.  There  seem,  as  it  were,  to  be 
lines  of  cleavage,  so  that  the  complex  pro- 
teins, under  the  influence  of  acids,  alkalies, 
high  temperatures,  and  various  enzymes, 
decompose  into  acids,  bodies  of  a  fatty 
nature,  aromatic  bodies, — which  all  contain 
nitrogen, — and  bodies  that  belong  to  the  carbo- 
hydrate group, — containing  no  nitrogen, — such 
as  starch  and  sugar.  Such  bodies  are  pro- 
duced when  proteins  are  split  up,  whether 
it  be  by  the  processes  of  the  chemist  in  the 
laboratory,  in  the  process  of  digestion  under 
the  action  of  the  digestive  enzymes,  or  in 
putrefaction  as  carried  on  by  many  micro- 
organisms, and  more  especially  by  the  Bac- 
terium termo,  a  minute  organism  found 
wherever  there  is  decay.  Proteins  are  ulti- 
mately resolved  into  certain  ammoniacal 
compounds  and  urea,  a  substance  abundant  in 
the  urine. 

40.     The  carbo-hydrates    are    the    starches 


MATTER   AND   ENERGY  83 

and  sugars.  They  consist  of  carbon,  hydrogen 
and  oxygen,  the  two  latter  elements  being  in 
the  proportions  that  form  water,  that  is, 
two  of  hydrogen  to  one  of  oxygen,  hence  the 
somewhat  inappropriate  name.  They  contain 
no  nitrogen.  They  are  usually  classified  into 
the  polysaccharides,  such  as  starch  and  glyco- 
gen  (an  animal  starch  found  in  the  liver), 
monosaccharides,  such  as  dextrose,  glucose  or 
grape  sugar  ;  and  disaccharides,  such  as  cane 
sugar,  lactose,  and  maltose.  When  cane 
sugar  is  inverted,  it  takes  up  water  and  is 
changed  into  equal  parts  of  dextrose  (grape 
sugar)  and  levulose  (fructose).  By  hydro- 
lysis of  starch  various  forms  of  dextrin  are 
formed.  Cellulose,  as  found  in  the  cell- 
walls  of  plants,  is  also  a  carbo-hydrate. 
Carbo-hydrates,  by  various  chemical  agencies, 
may  also  be  resolved  into  simple  substances, 
and  ultimately  into  carbonic  acid  and  water. 
41.  The  Fats  consist  of  a  combination  of 
a  fatty  acid  and  glycerine.  They  consist  of 
carbon,  hydrogen,  and  oxygen,  but  the  amount 
of  carbon  present  in  proportion  to  the  oxygen 
present  is  much  greater  than  in  carbo- 


84     PRINCIPLES   OF   PHYSIOLOGY 

hydrates.  When  oxidized,  as  by  burning,  they 
are  resolved  into  carbonic  acid  and  water, 
with  a  great  evolution  of  heat.  The  chief  fats 
are  tri-stearin,  tri-palmitin,  and  tri-olein. 
When  a  fat  is  acted  on  by  lipase  (an  enzyme), 
it  hydrolyses  and  splits  into  a  fatty  acid  and 
glycerine.  If  a  fat  is  acted  on  by  an  alkali 
a  soap  is  formed  and  glycerine  is  liberated. 
42.  Along  with  proteins,  carbo-hydrates,  and 
fats,  there  are  various  salts,  such  as  chloride  of 
sodium  (common  salt),  chloride  of  potassium, 
various  phosphates  of  soda,  potash,  lime,  and 
magnesia.  In  the  ash  of  organic  matters  we 
also  find  sulphur  and  iron  compounds,  but  these 
are  derived  not  from  inorganic  compounds 
of  these  elements,  but  from  decomposition  of 
the  proteins  It  is  doubtful  if  any  of  these 
inorganic  salts  exist  during  life  in  a  free  state  ; 
it  is  more  than  probable  that  they  are  usually 
combined  with  organic  bodies,  and  that  in 
this  way  they  take  their  part  in  vital  pheno- 
mena. The  proportions  of  the  various  salts, 
as  determined  by  chemical  analysis,  is  very 
uncertain.  It  may  be  that  certain  saline 
matters  are  simply  dissolved  in  the  colloidal 


MATTER  AND   ENERGY  85 

living  matter.  There  is,  however,  another 
way  in  which  they  may  be  taken  up,  when 
they  are  not  dissolved,  but  pass  into  the 
colloidal  matter  in  virtue  of  some  affinity  for 
it.  This  process  is  called  adsorption.  The 
electrical  state  of  the  colloid  influences  this 
process.  Adsorption  plays  an  important  part 
in  physiological  processes. 

43.  Finally    we    have    water,    the    general 
solvent,  and  the  medium  by  which  the  mole- 
cules of  the  other  bodies  are  brought  so  close 
together    as    to    permit    of    those    reciprocal 
actions  on  which  life  depends.     About  two- 
thirds  of  the  weight  of  the  body  consists  of 
water. 

44.  Chemical    Phenomena    of    Plant    Life. 
We  can  now  form  some  conception  of  the 
relation  of  matter  and  energy  in  the  living  body, 
and  we  shall  be  assisted  if  we  consider  the 
chemical  phenomena  of  plant  life  and  contrast 
these  with  what  happens  in  an  animal.     A 
plant  requires  ammoniacal  salts,  water  and 
carbonic    acid.     These    it    derives    from    the 
soil    and    the    air,    and    ammoniacal    com- 
pounds that  are  mainly  the  result  of  chemical 


86     PRINCIPLES   OF   PHYSIOLOGY 

operations  in  the  animal  body.  The  proto- 
plasm of  the  plant  combines  these  with  oxygen, 
forming  more  complex  chemical  compounds. 
Thus  by  means  of  chlorophyll,  and  under  the 
action  of  the  energy  of  light,  it  decomposes  the 
carbonic  acid  of  the  air,  retaining  the  carbon 
and  returning  the  oxygen  to  the  air.  The 
carbon  is  then  united  with  oxygen  and  hydro- 
gen to  form  starchy  substances,  which,  by  the 
action  of  an  amylolytic  ferment  (diastase),  may 
be  changed  into  sugars,  In  a  similar  way,  the 
ammoniacal  bodies  are  used  up  to  form  pro- 
teins. All  this  is  done  by  the  protoplasm  of 
the  plant  cell,  and  there  can  be  little  doubt  that 
the  formation  of  these  bodies  is  the  result  of 
chemical  operations  in  the  protoplasm,  which 
is  alive.  To  do  this  it  must  have  oxygen,  and 
it  must  get  rid  of  the  waste  body,  carbonic  acid. 
This  constitutes  the  true  respiration  of  a  plant, 
and  must  not  be  confused  with  the  chlorophyll 
action  above  referred  to.  The  plant  thus 
transforms  the  kinetic  energy  of  the  sun's 
rays  into  the  potential  energy  stored  up 
in  the  starch  and  in  the  protein  matter 
in  its  cells,  Fats  may  also  be  formed.  The 


MATTER   AND   ENERGY  87 

plant  protoplasm,  however,  while  it  performs 
this  operation,  also,  in  connection  with  its 
own  special  activities,  sets  free  kinetic  energy. 
Thus  certain  of  the  parts  of  plants  produce 
heat,  and  energy  may  appear  as  motion, 
when  rootlets  press  through  the  soil,  or  when 
certain  parts  move.  Still  the  main  relation  of 
plant  life  to  energy  is  that  it  stores  it  up,  or 
renders  it  potential. 

45.  Chemical  Phenomena  of  Animal  Life. 
The  activities  of  an  animal  are  mainly  of  an 
opposite  kind.  The  animal  lives  on  plants 
or  upon  the  tissues  of  other  animals.  Animal 
protoplasm  cannot  exist  on  ammoniacal 
compounds,  water,  and  saline  matters  alone. 
It  has  little  or  no  power  of  forming  those 
into  more  complex  substances.  But  it 
takes  proteins,  carbo-hydrates,  and  fats, 
and  along  with  saline  matters  and  water  it 
builds  these  up  into  its  own  protoplasm.  It 
may  possibly  use  them  to  some  extent 
directly,  that  is  to  say,  without  incorporation 
into  its  protoplasm,  but  this  is  doubtful. 
It  is  probable  that  there  is  a  true  incor- 
poration, but,  before  incorporation,  the 


88     PRINCIPLES  OF  PHYSIOLOGY 

proteins,  carbo-hydrates,  and  fats  must  be 
modified  by  digestive  processes,  So  far  the 
animal  protoplasm,  like  that  of  the  plant, 
has  been  storing  energy  There  is  now  a 
reversal  of  the  operation  Under  various 
stimuli,  which  may  be  the  nervous  impulse, 
or  a  mechanical,  thermal,  or  electrical 
stimulation,  the  protoplasm  either  contracts 
(as  in  muscle)  or  is  the  seat  of  chemical 
operations  (as  in  a  secreting  cell  or  an  electrical 
organ),  and  energy  is  set  free  as  motion  and 
heat,  or,  it  may  be,  luminous  or  electrical 
energy  This  implies  decompositions  and 
oxidations,  and  requires  oxygen  from  the  air. 
The  splitting  up  of  the  complex  protoplasm 
causes  the  formation  of  simpler  bodies.  These 
may  be  again  and  again  further  oxidized  into 
simpler  compounds,  always  with  the  evolution 
of  energy,  as  heat,  until  ultimately  we  reach 
simple  ammonia-like  bodies,  urea,  and  water. 
Thus  the  protoplasm  of  animal  cells  is  chiefly 
engaged  in  the  liberation  of  potential  into 
kinetic  energy.  Both  plant  and  animal  take 
part  in  both  processes.  In  the  plant  there 
are  oxidations  as  well  as  reductions,  but 


MATTER  AND   ENERGY  89 

mainly  reductions  ;  in  the  animal  there  are 
reductions  as  well  as  oxidations,  but  mainly 
the  latter.  Both,  as  in  processes  of  develop- 
ment, convert  potential  into  kinetic  energy, 
but  in  the  plant  the  conversion  is  mainly  from 
kinetic  into  potential,  while  in  the  animal 
the  action  is  far  and  away  a  passage  from 
potential  into  kinetic  energy.  Thus  the  plant 
world  is,  physiologically,  the  complement  of  the 
animal  world 


CHAPTER  VII 

INCOME  OF  MATTER.   THE  ABSORPTION 
OF  FOOD  STUFFS 

46.  As  all  forms  of  vital  activity  cause  a 
certain  amount  of  tear  and  wear  owing  to  the 
breaking  down  of  living  matter,  or,  in  other 
words,  the  decomposition  of  complex  organic 
substances  into  simpler  ones, — usually  accom- 
panied either  with  the  withdrawal  of  oxygen 
(reductions)  or  with  the  union  of  oxygen  with 
oxidizable  substances  (oxidations), — matter 
must  be  supplied  in  the  form  of  food.  Food 
stuffs  however,  as  a  rule,  are  very  unlike  the 
tissues  of  the  body.  Observation  also  shows 
that  animals  may  live  on  food  stuffs  that  are 
very  unlike  in  appearance.  Thus  an  ox  can  live 
upon  grass,  a  horse  on  hay  and  oats,  a  rabbit 
on  turnips  or  carrots,  a  tiger  and  other  flesh- 
eating  animals  on  flesh  of  various  kinds. 

Man  is  so  constituted  as  to  find  a  mixed  diet 
90 


INCOME  OF  MATTER  91 

most    suitable.     All    mammals    begin    their 
existence   on   milk.     The  tissues  of  a  chick 
are    built    up    out    of    materials    contained 
within    an    egg.      If,    however,    we    analyze 
food   stuffs,  or   diets   that   are   known   from 
experience  to  suit  all  dietetic  requirements,  we 
find  they  always  contain  representatives  of 
the    five    proximate    constituents    found   in 
the    tissues    of    the    body,    and    which    we 
have  considered.     Thus  a  suitable  dietary  for 
almost  any  animal,    and   certainly  for  men, 
always  contains  proteins,  carbo-hydrates,  fats, 
saline  matters  and  water.     Other  substances, 
such  as  the  condiments  that  are  often  added, 
are  merely  adjuncts  to  the  diet.     Thus  milk 
contains  more  than  one  protein  substance, 
the  chief  one  being  caseinogen,  which  yields, 
when  acid  or  rennin  is  added  to  the  milk,  a 
protein,  casein,  the  chief  constituent  of  curd ; 
a   carbo-hydrate    as   sugar   of   milk ;    a   fat, 
or  rather  several  fatty  matters  that  all  together 
form  butter ;   various  salts  (chiefly  chloride  of 
sodium  and  phosphate  of  lime) ;    and  water. 
These  proximate  constituents   are  found  in 
varying  amounts  in  different  articles  of  food 


92     PRINCIPLES   OF   PHYSIOLOGY 

met  with  in  dietaries.  Thus,  butcher  meat 
abounds  in  protein  and  fat,  potatoes  in  starch 
(a  carbo-hydrate) ;  and  vegetable  oils  and 
animal  fat  are  rich  in  fat.  By  combinations 
of  these,  a  suitable  dietary  is  formed,  and 
experience  has  taught  mankind,  even  in 
savage  conditions,  empirically  to  combine 
such  substances.  Further,  science  has  shown 
that  a  suitable  dietary  supplies  the  requisite 
amount  of  carbon  and  the  requisite  amount 
of  nitrogen  to  make  up  for  the  daily  loss  of 
carbon  eliminated  chiefly  by  the  lungs,  as  car- 
bonic acid,  and  of  nitrogen  thrown  out  by  the 
kidneys  mainly  as  urea. 

47.  In  order  to  become  incorporated  with 
the  living  tissues,  food  stuffs  must  pass 
through  a  series  of  elaborate  physical  and 
chemical  processes,  the  object  of  which  is 
to  render  them  soluble  and  suitable  for  ab- 
sorption into  the  blood.  These  processes 
constitute  Digestion.  The  food  is  broken 
down  and  mixed  in  the  mouth  with  saliva 
so  as  to  form  a  pulpy  mass.  Such  matters 
as  saline  substances  may  be  at  once  dissolved, 
and  the  whole  process  is  facilitated  by  the 


INCOME  OF  MATTER  93 

heat  of  the  mouth.  Mastication  is  a  physical 
process  carried  on  by  the  movements  of  the 
jaws  bearing  the  teeth.  Saliva  is  a  fluid 
poured  forth  from  three  pairs  of  salivary 
glands  and  by  numerous  small  glands  in 
the  membrane  lining  the  various  parts  of  the 
mouth.  Chemically,  the  saliva  acts  only  on 
carbo-hydrates  in  the  form  of  starch:  it  has 
no  chemical  action  on  proteins  or  fats.  The 
saliva,  in  addition  to  being  a  watery  solvent, 
contains  an  enzyme  called  ptyalin,  which  con- 
verts starch  into  dextrose  or  grape  sugar,  thus 
rendering  the  carbo-hydrate  soluble.  The 
saliva  also  lubricates  the  mouthful  with 
mucus,  and  thus  facilitates  swallowing. 

48.  The  food  is  then  swallowed  (Degluti- 
tion) and  by  a  muscular  mechanism  (con- 
trolled by  nerves)  it  is  prevented  from  escaping 
by  the  mouth,  or  into  the  nose  by  the  posterior 
apertures  of  the  nostrils,  or  into  the  chink 
between  the  true  vocal  cords  which  is  the 
entrance  into  the  trachea,  or  windpipe,  and 
the  respiratory  passages.  It  is  propelled 
into  the  gullet  (oesophagus),  and  carried  into 
the  stomach  by  a  series  of  contractile  move- 


94     PRINCIPLES   OF   PHYSIOLOGY 

ments.  The  greater  part  of  this  nervo-muscu- 
lar  mechanism  is  beyond  the  control  of  the 
will,  after  the  food  has  passed  sufficiently  far 
into  the  mouth,  and  so  exquisite  are  its  adap- 
tations that  only  when  food  is  swallowed 
hurriedly,  or  with  great  gulps  of  liquid,  is  there 
any  danger  of  the  matter  entering  the  wrong 
passage. 

49.  In  the  stomach,  which  is  simply  a  special 
enlargement  of  the  alimentary  canal,  the  food 
is  subjected  to  three  processes : — (1)  The 
action  of  a  temperature  of  about  98°  F.  ; 
(2)  a  churning-like  motion  produced  by  slow 
contractions  of  the  muscular  walls  by  which  the 
food  is  thoroughly  mixed  with  the  special 
secretion  of  the  stomach,  the  gastric  juice  ; 
and  (3),  the  chemical  action  of  the  gastric 
juice  itself.  This  juice  is  secreted  by  numerous 
tubular  glands  in  the  mucous  membrane, 
It  is  a  clear  watery  fluid  containing  a 
minute  quantity  of  various  salts  in  solution, 
a  small  amount  (*2  per  cent.)  of  hydrochloric 
acid,  and  a  special  enzyme,  pepsin.  It  is  only 
secreted  in  ordinary  circumstances  when  food 
enters  the  stomach,  and  by  the  contractions 


INCOME   OF  MATTER  95 

of  the  walls   it    is    thoroughly    mixed    with 
the   contents.     The   action   of   pepsin   is   on 
proteins,  converting  these  into  a  more  special- 
ized form  of  protein,  termed  peptone ;    and 
in  this  action  it  is  assisted  by  the  free  hydro- 
chloric acid  of  the  gastric  juice.     The  juice, 
by  acting  on  the  walls  of  the  cells  in  the  food 
stuffs,  liberates  fatty  matters,  or  granules  of 
more  or  less  cooked  starch,  and  thus  these  are 
prepared  for  further  digestion.    Saline  matters, 
that  may  have  escaped  the  solvent  action  of 
the  saliva,  are  dissolved.     Protein  food  stuffs, 
as  in  cooked  butcher  meat,  are  disintegrated 
into    fibres    and    small    morsels;    these   are 
then   acted    on   by   the   pepsin    and   hydro- 
chloric acid.     The  result  is  the  formation  of 
a  semi-digested  mass,  the  chyme,  which,  as  it 
is  formed,  escapes  through  the  pyloric  opening 
into  the  first  portion  of  the  small  intestine,  the 
duodenum.     During  the  digestive  process  in 
the  stomach,  the  orifices  at  the  lower  end  of  the 
oesophagus  and  at  the  beginning  of  the  small 
intestine,    the    pyloric   opening,   are    tightly 
closed  by  sphincters.     Thus  a  portion  of  any 
protein  in  the  food  is  converted  into  simpler 


96     PRINCIPLES   OF   PHYSIOLOGY 

and  more  soluble  forms  of  protein  called 
peptones,  and  the  mass,  containing,  in  addition 
to  peptones,  undigested  protein  matters, 
sugars,  starch-granules  that  have  escaped 
the  action  of  the  saliva,  fats  in  a  more  or  less 
fluid  state,  salts  in  solution,  constitutes 
the  chyme.  It  is  doubtful  if  absorption 
to  any  extent  occurs  in  the  stomach.  The 
free  hydrochloric  acid  of  the  juice  may 
cause  some  proteins  to  swell  and  become 
gelatinous-looking,  forming  what  is  called 
syntonin.  The  acid  also,  to  some  extent, 
destroys  bacteria  that  are  almost  inevitably 
swallowed  with  the  food,  but  many  escape 
into  the  bowel.  The  gastric  juice  of  young 
mammals  also  contain  rennin,  a  milk-curdling 
enzyme.  Thus  the  special  action  of  the  gastric 
juice  is  on  proteins. 

50.  The  Intestine.  The  chyme  is  propelled 
into  the  small  intestine,  which  is  of  great 
length;  in  it  two  processes  occur:  (1)  the 
completion  of  digestion,  and  (2)  the  absorp- 
tion of  digested  matters.  Near  the  beginning 
of  the  small  intestine,  in  the  duodenum,  two 
fluids  mix  with  the  chyme,  the  bile,  formed 


INCOME   OF  MATTER  97 

by  the  liver,  and  the  pancreatic  juice,  secreted 
by    a    gland    similar    in    structure    to    the 
salivary  glands,    called  the  pancreas.      The 
bile  is  constantly  being  formed  by  the  liver, 
and  passes  drop  by  drop  from  the  end  of  the 
bile-duct    into    the    duodenum.     This    fluid 
does  not  take  an  active  part  in  the  digestion 
of  the  constituents  of  food,  and  it  may  be  re- 
garded more  as  an  excretion  or  waste  product 
of  the  complicated  chemical  processes  occur- 
ring in    the    liver.      Still,    as    it    is    poured 
into  the  small  bowel  so  near  its  beginning, 
it  must  exert  some  influence.     That  influence 
may  or  may  not  be  beneficial  according  to  its 
quantity.    If  in  great  amount  it  may  pass  back 
into  the  stomach  and  partly  arrest  the  digestive 
process  there,  as  happens  in  a  bilious  attack  ; 
or   it   may   to    some    extent    interfere   with 
processes  in  the  bowel  if  in  excessive  amount, 
and    it    appears    to     act    as     a    stimulant 
to   the   musculo-nervous   mechanism   of   the 
bowel  by  which  the  chyme  is  propelled  on- 
wards.    In   excess   it   may   cause   diarrhoea. 
A  portion  of  the  bile  may  be  stored  in  the 
gall  bladder,  an  organ,  however,  that  does  not 


98     PRINCIPLES  OF  PHYSIOLOGY 

appear  to  be  indispensable,  as  many  animals 
have  no  such  reservoir. 

Along  with  the  bile  from  the  liver,  the 
pancreatic  fluid  enters,  often  by  a  duct  formed 
by  the  confluence  of  the  ducts  of  the  two 
glands  This  fluid  is  secreted  only  during 
the  digestive  process,  and  the  secretion  appears 
to  be  stimulated  and  modified  in  character 
by  a  special  enzyme  in  the  duodenum  called 
secretin,  a  remarkable  example  of  a  ferment 
body  acting  so  as  to  excite  the  activity  of 
another  enzyme-forming  gland.  Another 
enzyme,  known  as  entero-kinase,  formed  in 
the  duodenum,  appears  to  facilitate  the 
action  of  one  of  the  pancreatic  ferments, 
trypsin  The  pancreatic  fluid  is  assumed 
to  contain  three  ferments :  (1)  one  acting 
on  proteins  and  peptones,  called  trypsin, 
splitting  those  up  into  simpler  bodies, 
mainly  such  as  leucin  and  tyrosin  (crystal- 
lizable  bodies) ;  (2)  another,  amylopsin,  acting 
on  the  starch,  cooked  or  raw,  which  has  escaped 
the  saliva,  changing  it  into  grape  sugar ;  and 
(8)  one  that  acts  on  fats,  lipase,  splitting  them 
up  into  glycerine  and  a  fatty  acid,  while  the 


INCOME   OF  MATTER  99 

free  acid  immediately  unites  with  alkalies  in 
the  bowel,  potash  and  soda,  to  form  highly 
soluble  soaps.  The  pancreatic  juice  also  con- 
tains a  milk-curdling  ferment.  The  action  on 
proteins  is  to  split  up  the  protein  molecule  into 
simpler  soluble  substances,  such  as  leucin, 
tyrosin,  and  simpler  bodies  known  as  amino- 
acids.  Some  of  the  bodies  so  formed  may  be 
absorbed  into  the  blood,  while  any  excess 
is  probably  voided  in  the  faeces. 

51.  The  whole  length  of  the  small  intestine 
contains  numerous  glands,  those  in  the  duo- 
denum termed  the  glands  of  Brunner,  while 
the  others  are  known  as  Lieberkuhn's  glands. 
These    glands    secrete    the    intestinal    juice, 
which  has  a  feeble  action  somewhat  resem- 
bling that   of   the   pancreas.     It  contains  a 
special  enzyme,  erepsin.    (See  p.  76.)     There 
is  also   present   an  enzyme  called   invertase, 
which  splits  up  cane  sugar  into  dextrose  and 
levulose. 

52.  The    great    intestine,    which    is    much 
shorter  and  wider  than  the  small,  may  be 
regarded    as    a    receptacle    for     the    refuse 
materials  of  food  stuffs  that  have  not  been 


100  PRINCIPLES  OF  PHYSIOLOGY 

digested,  and  for  various  substances  excreted 
by  numerous  tubular  glands.  The  secretions 
of  the  great  bowel  do  not  take  an  active  part 
in  true  digestion.  Putrefactive  processes  also 
are  carried  on,  even  in  the  small  bowel,  and 
still  more  in  the  larger  bowel,  and  these 
processes,  due  to  the  activities  of  numerous 
bacteria,  still  further  split  up  the  protein 
molecules,  with  the  production  of  offensive 
smelling  bodies,  indol,  skatol,  phenol,  etc. 
These  bodies,  by  uniting  with  sulphuric 
acid  arising  from  sulphates  (originating  from 
the  sulphur  of  proteins),  form  etherial  sul- 
phates, such  as  indoxyl-sulphate  of  potassium. 
This  body  is  called  indican,  and  is  voided 
in  the  urine.  Such  fermentative  and  putrefac- 
tive processes,  all  due  to  specific  organisms, 
also  attack  carbo-hydrates  and  fats,  producing 
lactic  acid,  butyric  acid,  sulphuretted  hydro- 
gen, carbonic  acid,  and  other  substances. 
The  absorption  of  these  may  cause  a  kind  of 
auto-poisoning  of  the  individual. 

53.  It  will  be  seen  that  all  the  constituents 
of  food  are  now  soluble  and  ready  for  absorp- 
tion, This  is  accomplished  mainly  in  the 


INCOME  OF  MATTER         101 

small  intestine,  partly  by  the  blood  vessels, 
and  partly  by  special  absorbents,  the  lacteals. 
Covering  the  whole  of  the  mucous  membrane 
of  the  small  bowel  there  are  innumerable 
small  finger-like  processes,  like  the  pile  of 
velvet.  Each  process  is  a  little  organ  called 
a  villus.  In  the  centre  of  each  villus  there  is 
a  tube,  the  outer  end  of  which  communicates 
with  numerous  minute  channels  ;  this  is  the 
commencement  of  the  absorbent  system.  By 
the  confluence  of  the  bases  of  these  tubes  a 
network  of  fine  tubes,  running  in  the  mesen- 
tery (or  web  connecting  the  bowel  with  the 
wall  of  the  abdomen)  is  formed,  and  these 
tubes,  by  confluence,  form  larger  and  larger 
tubes  until  they  reach  certain  gland-like 
structures,  the  mesenteric  glands.  The  ducts 
of  these  glands,  now  called  mesenteric  lymph- 
atic glands,  pass  to  a  special  receptacle,  the 
receptaculum  chyli,  and  from  it  a  large 
duct,  the  thoracic  duct,  runs  up  through 
the  thorax,  and,  at  the  root  of  the  neck, 
on  the  left  side,  opens  obliquely  into  the 
venous  system,  just  at  the  confluence  of 
the  internal  jugular  vein,  carrying  blood 


102  PRINCIPLES  OF  PHYSIOLOGY 

from  the  head  and  neck,  with  the  superior 
subclavian  vein,  coming  from  the  left  arm. 
This  lacteal  system  (so  called  because,  during 
the  digestion  of  fat,  it  is  filled  with  a  milky 
like  fluid,  the  chyle)  is  the  absorbent  system 
mainly  for  fats,  taken  up,  either  as  a  fine 
emulsion  or  as  soaps,  from  the  bowel  by  the 


54.  In  each  villus,  between  its  epithelial 
covering  and  the  centre,  in  addition  to  the 
fine  absorbents  already  noticed,  there  is  a 
rich  plexus  of  capillary  blood  vessels.  These 
absorb  all  soluble  matters,  such  as  peptones, 
sugars,  possibly  soaps,  saline  matters,  water, 
and  any  other  substances  in  solution.  The 
blood  thus  circulating  in  the  villi  is  gathered 
up  by  veins,  and  these  form  the  mesenteric 
system  of  vessels.  Blood  is  thus  gathered 
from  all  parts  of  the  intestinal  canal, 
stomach,  small  intestine,  and  large  intestine, 
and  by  the  vessels  forming  the  portal  system 
and,  by  a  large  vein  called  the  portal 
vein,  it  is  carried  to  the  liver  :  It  will  thus 
be  seen  that  all  the  products  of  digestion, 
except  emulsive  fats,  and  all  soluble  matters, 


INCOME   OF  MATTER  103 

are  in  the  first  instance  carried  to  the  liver. 
In  that  organ,  the  largest  gland  in  the  body, 
and  the  seat  of  intense  physiological  activities, 
intricate  chemical  processes  occur.  One  of 
the  results  of  these  is  the  formation  of  bile, 
which  may  be  regarded  as  a  waste  product 
arising  from  the  chemical  processes  occurring 
in  the  gland.  The  blood,  laden  with  matters 
absorbed  from  the  alimentary  canal,  and 
modified  by  the  cells  in  the  liver,  issues  from 
the  organ  by  the  hepatic  vein,  which  then 
pours  the  blood  into  the  venous  system.  The 
matters  thrown  out  in  the  bile  will  be  con- 
sidered in  connection  with  excretion. 

Thus  it  will  be  seen  that  all  the  matters 
absorbed  in  the  alimentary  canal  ultimately 
reach  the  venous  system.  They  all  contribute 
to  the  making  of  blood.  The  fatty  matters 
absorbed  by  the  villi  are  modified  by  the 
mesenteric  glands.  They  feed  the  protoplasm 
of  these  glands,  which  then  gives  off  leuco- 
cytes or  colourless  corpuscles.  These  glands 
are  abdominal  lymphatic  glands,  and  they 
share  with  other  lymphatic  glands  (found 
in  many  parts  of  the  body)  in  the 


104  PRINCIPLES  OF  PHYSIOLOGY 

production  of  leucocytes.  Finally,  matters 
that  are  undigested ;  chemical  substances 
arising  from  proteins  that  have  not  been 
absorbed;  special  matters  secreted  by  the 
glands  of  the  great  intestine  of  which  we  know 
little ;  countless  bacteria ;  and  earthy  matters, 
such  as  phosphates  of  lime  and  magnesia, — 
are  voided  in  the  faeces, 

55  There  are  several  interesting  questions 
as  to  absorption  that  must  be  noticed,  as  an 
answer  to  them  takes  us  to  first  principles. 
Water  and  soluble  salts  are  absorbed  un- 
changed. The  salts  may  be  adsorbed.  Carbo- 
hydrates are  all  absorbed  as  sugars,  and 
they  are  carried  to  the  liver  and  are  there 
transformed  into  glycogen  (a  kind  of  animal 
starchy  substance),  and  stored  for  a  time 
No  doubt  some  may  pass  along  in  the 
blood  stream,  and  be  at  once  used  by  the 
tissues.  It  is  highly  probable  that  when 
no  fresh  sugar  is  coming  from  the  intestine 
sugar  is  supplied  from  the  liver  to  the 
tissues,  that  is  to  say  glycogen  is  changed 
by  a  liver  enzyme  into  sugar,  and  this  is  at 
once  washed  away.  There  are  good  grounds 


INCOME  OF  MATTER  105 

for  the  view  that  leucocytes  take  some 
part  in  these  processes,  as  we  find  always  a 
great  increase  of  these  cells  during  absorp- 
tion. Fat  we  have  seen  to  be  absorbed  by 
the  lacteals  of  the  villi.  Ultimately  the  mole- 
cules of  fat  reach  the  protoplasm  in  lymphatic 
glands,  and  are  there  changed  ;  but  probably 
a  portion  of  the  fat  is  seized  by  special  cells 
in  connective  tissue  (fat  cells),  and  is  stored 
there  in  a  liquid  state.  How  it  is  used  up  by 
the  tissues  is  still  obscure,  but  we  may  be 
sure  it  contributes  to  the  making  of  proto- 
plasm in  muscular,  and  more  especially  in 
nervous,  tissues. 

It  is  also  difficult  fully  to  explain  the 
changes  that  happen  in  proteins.  At  one 
time  it  was  supposed  that  peptones  were 
absorbed  as  such,  and  thus  entered  the 
portal  circulation.  This  view  has  been 
abandoned,  and  now  it  would  appear  that 
protein  matter  is  absorbed  in  simpler  forms 
than  peptones,  and  especially  as  amino- 
acids.  These  are  acids  belonging  to  the 
group  known  to  chemists  as  fatty  acids, 
substitution  compounds  in  which  one  of  the 


106  PRINCIPLES  OF  PHYSIOLOGY 

hydrogens  of  the  radicle  is  replaced  by  a 
molecule  containing  two  atoms  of  hydrogen 
and  one  of  nitrogen.  Thus  take  caproic  acid, 
one  of  the  fatty  acid  series.  It  is  represented 
by  the  chemical  formula  C5HirCOOH; 
substitute  for  one  of  Hn  a  group  NH2,  and 
we  have  C5H10.NH2.COOH,  or  amino- 
caprcic  acid,  a  well-known  body  called 
leucin.  It  is  important  to  note  that  these 
amino-acids,  of  which  there  is  a  large  num- 
ber known  to  chemists,  are  always  among  the 
final  products  of  the  decomposition  of  proteins. 
Hence  it  was  inferred  that  proteins  were  ab- 
sorbed as  amino-acids.  These,  however,  have 
not  been  found  in  the  blood,  possibly  owing 
to  great  technical  difficulties,  and  it  is  still 
a  matter  undecided  as  to  (1)  whether  proteins 
are  so  absorbed,  and  (2)  how  and  where  they 
are  re-transformed  into  the  proteins  of  the 
blood.  It  is  a  fact,  however,  that  they  all 
pass  to  the  liver,  and  that  during  the  absorp- 
tion of  proteins  the  nitrogen  in  the  blood 
increases. 

Further,  it  would  seem  that  protein  matter 
may  be  used  up  in  two  ways.  A  certain  portion 


INCOME  OF  MATTER  107 

in  the  blood  is  carried  to  the  tissues,  and  there 
it  is  metabolized  for  the  upbuilding  of  proto- 
plasm. As  we  now  know  there  are  many 
tissue-enzymes,  it  may  be  that  in  the  living  cell 
these  enzymes,  in  a  sense,  re-digest  this  portion 
of  proteid,  changing  it  again  into  amino-acid 
bodies,  and  that  these  are  used  for  upbuilding 
protoplasm.  But  there  may  be  an  excess  of 
protein,  and  it  may  then  be  thrown  aside  as 
creatin  and  other  bodies  found  in  muscle-juice. 
This  portion  we  may  call  tissue-protein.  Prob- 
ably it  has  characters  of  its  own  different  from 
those  of  the  other  portion  of  the  protein  which 
we  must  now  consider.  This  second  portion  of 
protein,  which  we  may  term  excess-protein,  is 
decomposed  by  cells  in  the  liver,  passes  prob- 
ably through  many  stages  and  is  ultimately 
voided  by  the  kidneys  in  the  form  of  urea.  A 
rich  protein  diet  always  causes  an  increase  in 
the  amount  of  urea  eliminated.  There  are,  how- 
ever, critical  objections  to  this  view.  Is  this 
complicated  process  merely  an  arrangement 
for  getting  rid  of  excess  of  protein  ?  One 
can  hardly  imagine  this  to  be  the  case.  At 
present  we  are  not  yet  in  a  position  to  state 


108   PRINCIPLES   OF  PHYSIOLOGY 

what  occurs  in  a  hepatic  cell.  The  process  may 
not  be  a  series  of  processes, — one  having  to  do 
with  the  storage  of  glycogen,  another  with  the 
making  of  substances  in  the  bile,  such  as  bile 
pigments,  bile  salts,  cholesterin,  etc., — but  one 
synthesis  and  one  decomposition. 


CHAPTER    VIII 

THE    BLOOD.       ITS    RELATION    TO    THE    LIVING 
TISSUES 

56.  WE  have  seen  that  the  various  food  stuffs 
rendered  soluble  by  the  processes  of  digestion 
are  taken  into  the  blood.  This  fluid  is  brought 
by  the  smaller  vessels,  the  capillaries,  into 
close  proximity  to  all  the  elements  of  the 
living  tissues.  From  the  blood  vessels  a  fluid 
passes  out  through  their  walls  and  permeates 
all  the  tissues,  bathing  their  elements,  so  that 
there  is  much  truth  in  the  aphorism  that  the 
elements  of  the  living  tissues,  and  more  especi- 
ally the  living  cells,  live  like  aquatic  organ- 
isms, that  is  to  say,  they  live  in  a  fluid,  and 
their  lives  and  activities  depend  on  inter- 
changes between  them  and  the  fluid.  This 
fluid  is  the  lymph.  Some  of  it  is  used  up  in 
the  nutrition  of  the  tissues,  and  the  surplusage, 
now  containing  in  solution  matters  derived 
109 


110  PRINCIPLES  OF  PHYSIOLOGY 

from  the  breaking  up  of  substances  in  the 
tissues — substances  derived  from  their  physio- 
logical tear  and  wear — is  carried  off  by  a  drain- 
age system  of  tubes,  the  lymphatics.  The 
lymph,  however,  is  not  thrown  out  of  the 
body  as  useless,  but,  as  in  the  economy  of  a 
well-arranged  manufactory,  it  is  utilized ;  it 
is  carried  to  lymphatic  glands  found 
in  many  parts  of  the  body  and  of  the 
same  class  as  those  already  alluded  to  as 
existing  in  the  mesentery.  By  these  glands 
it  is  used  up,  elaborated,  as  is  often 
said,  so  as  to  nourish  the  protoplasm 
of  those  organs,  and  it  is  ultimately 
poured  into  the  blood,  either  along  with 
the  chyle  in  the  thoracic  duct,  or  by  a 
special  duct,  the  lymphatic  duct,  which 
joins  the  venous  system  at  the  root  of 
the  neck  on  the  right  side.  Thus  the 
blood  receives  all  the  lymph  and  all  the 
chyle.  It  also  receives  cellular  elements 
from  the  lymphatic  glands,  from  the  kind  of 
tissue  called  lymphoid  or  adenoid  tissue, 
found  in  many  organs  and  beneath  many 
mucous  membranes,  and,  in  particular,  from 


THE  BLOOD  111 

the  red  marrow  found  in  the  cavities  in  the 
bones.  It  also  receives  oxygen  from  the  air 
by  the  process  of  respiration.  The  blood  also 
receives  matters  that  may  be  absorbed  from 
many  surfaces,  both  internal  and  external, 
such  as  the  pleural  and  peritoneal  cavities. 
The  blood  is  therefore  a  highly  complex 
fluid.  It  must  be  regarded  not  so  much  as 
a  fluid  as  a  complex  tissue,  and  as  the  physical 
condition  of  its  cellular  constituents,  the  blood 
corpuscles,  as  well  as  the  nutrition  of  the  tissues 
to  which  it  supplies  lymph,  depends  on  it, 
we  find  that  it  varies  very  little  either  in  its 
physical  characters  or  in  its  chemical  constitu- 
tion. Thus  its  specific  gravity  and  its 
viscosity  vary  within  very  narrow  limits. 
Matters  coming  to  it  by  the  channels  above 
indicated  are  constantly  being  used  up  by 
the  tissues  ;  so  that,  although  a  considerable 
amount  of  these  matters  enters  the  blood  daily, 
the  percentage  amount  of  any  one  of  them  is, 
as  a  rule,  small.  Again,  matters  that  are  waste 
products — and  which  would  be  injurious  to 
living  tissues,  if  they  accumulated  above  a 
small  percentage — are  continually  being  elimi- 


112  PRINCIPLES  OF  PHYSIOLOGY 

nated  by  various  excreting  organs.  Thus 
the  blood  does  not  vary  much  either  in  quantity 
or  quality,  a  physiological  condition  of  great 
importance. 

57.  As  already  mentioned,  the  blood  is  a 
highly  complex  fluid.  It  contains  three 
kinds  of  corpuscles,  (1)  red  corpuscles,  or 
erythrocytes,  (2)  white  or  colourless  corpuscles, 
(leucocytes),  of  which  there  are  several  varie- 
ties ;  and  (3)  minute  particles  called 
blood  plates.  The  red  corpuscles,  chiefly 
concerned  in  respiratory  exchanges,  exist 
in  enormous  numbers, — in  human  blood 
amounting  to  as  much  as  five  million 
in  a  drop  of  blood  about  one-twenty- 
fifth  of  an  inch  in  diameter.  The  white 
cells  probably  perform  several  functions, 
They  may  imbibe  certain  matters  from 
the  fluid  of  the  blood  and  elaborate  these 
into  other  substances.  By  their  power  of 
spontaneous  amoeboid  movement  they  may 
seize  upon  and  digest  worn  out  effete  red  cells, 
or  micro-organisms  that  in  many  diseases  find 
their  way  into  the  blood. 

58.  Recent    observations    on    the    blood, 


THE  BLOOD  113 

mostly  by  way  of  experiment,   have  shown 
that  in  the  blood  there  are  substances  which 
are  of  physiological  importance  although  their 
quantities  may  be  so  small  as  to  be  beyond 
our    present    methods    of    analysis.     These 
bodies  seem  to  act  as  chemical  defensive  agents 
against  disease.    It  is  well  known  that  the  leu- 
cocytes act  as  phagocytes,  that  is  they  seize, 
hold,  and  devour  bacteria  and  other  micro- 
organisms.    But,  in  addition  to  this  phago- 
cytic  action  of  leucocytes,  the  fluid  of  the  blood 
contains    substances    that    are    bactericidal. 
These  substances,  probably  protein  in  their 
character,  are  destroyed  by  heating  the  blood 
for  an   hour  to   55°   C.     Possibly   they   are 
derived  from  leucocytes.     They  may  be  called 
bacterio-lysins.     Other  substances  in  the  blood 
may  have  the  power  of  destroying  red  cor- 
puscles.    Thus  the  blood  serum  of  one  animal 
has  the  power  of  dissolving  the  red  corpuscles 
of  another  species.     Such  bodies  are  called 
haemolysins. 

The  importance  of  these  bodies  is  now 
generally  recognized.  Bacteria  or  bacilli  of 
many  kinds,  if  they  find  entrance  into  the 


114   PRINCIPLES  OF  PHYSIOLOGY 

body,  cause  disease,  either  by  multiplying  in 
enormous  numbers  or  by  producing  substances, 
called  toxins,  which  act  as  poisons.  A  toxin 
is  probably  of  the  nature  of  a  protein  or 
proteose,  and  usually  there  is  associated  with 
it  another  body,  called  an  antitoxin,  sad  to 
be  of  the  nature  of  a  globulin.  Toxin  and 
antitoxin  neutralize  each  other,  so  that  a 
mixture  injected  into  an  animal  may  produce 
no  effect.  By  a  system  of  inoculating  a 
healthy  horse  with  small  but  increasing  doses 
of  the  diphtheria  virus,  the  serum  of  the 
animal  by  and  by  contains  a  large  amount  of 
antitoxin,  and  the  injection  of  this  serum  in  a 
case  of  diphtheria  may  save  life  by  neutralizing 
the  toxin  of  the  disease.  Sera  prepared  in  this 
way  are  now  used  in  practical  medicine  with 
beneficial  effects.  Further,  they  may  confer 
immunity,  that  is  to  say,  the  injection  of  such 
fluids  may  protect  against  attacks  of  the 
disease.  Thus  the  body  may  be  protected 
against  the  invasion  of  specific  organisms  by 
the  phagocytic  action  of  leucocytes,  by  the 
globulicidal  action  of  various  substances  in 
the  blood,  and  by  the  formation  of  antitoxin. 


THE  BLOOD  115 

There  may  also  be  present  in  the  blood  sub- 
stances called  agglutininS)  that  arrest  the 
movements  of  bacteria  and  throw  them 
into  masses  or  clumps,  and  in  this  con- 
dition they  are  more  readily  devoured  by 
leucocytes.  Lastly,  there  are  substances 
known  as  opsonins,  that  also  appear  to 
increase  the  phagocytic  power  of  leucocytes. 
The  true  nature  of  these  chemical  sub- 
stances is  unknown.  They  are  probably 
proteins,  but  whether  they  are  different 
substances  or  modifications  of  one  substance 
s  a  question  to  be  answered  by  further  re- 
search. The  history  of  this  obscure  subject 
is  a  striking  illustration  of  the  complexity 
of  the  physiological  processes  that  may 
possibly  occur  in  the  blood. 

59.  The  blood  is  rich  in  proteins,  especially 
in  the  form  of  a  variety  of  albumen  and  of  a 
protein  substance  known  as  serum  globulin 
or  fibrinogen.  It  contains  traces  of  many 
other  substances.  If  we  examine  the  blood 
as  it  circulates  in  the  capillaries,  under 
the  microscope,  we  see  that  the  fluid,  liquor 
sanguinis,  is  an  almost  colourless  fluid,  and 


116   PRINCIPLES  OF  PHYSIOLOGY 

that  the  corpuscles,  in  single  file,  are 
carried  along  by  the  stream.  When  shed, 
however,  it  quickly  coagulates,  that  is  it 
clots,  and  the  clot,  in  a  suitable  vessel,  is 
soon  surrounded  by  and  floats  in  a  serum. 
This  power  of  clotting  no  doubt  is  a  salutary 
function,  as  when  vessels  have  been  accident- 
ally cut,  they  are,  as  a  rule,  soon  plugged  by 
the  clot,  and  bleeding  ceases.  Much  investi- 
gation has  been  expended  on  the  phenomenon 
of  clotting,  a  process  somewhat  analogous  to 
the  clotting  of  milk  when  it  sours,  from  the 
formation  of  lactic  acid,  or  when  acted  on  by 
the  ferment  of  rennet.  The  milk  separates  into 
curd  and  whey ;  the  blood  separates  into  serum 
and  clot.  A  clot  consists  of  blood  corpuscles 
and  a  substance  called  fibrin.  If  we  place 
a  piece  of  blood  clot  under  a  water  tap,  we  can 
wash  out  the  corpuscles  and  we  obtain  fibrin 
in  the  form  of  a  yellowish  fibrous  material. 
It  is  evident  that  the  formation  of  fibrin,  which 
entangles  the  corpuscles  in  its  fibrous  meshes, 
produces  a  blood  clot.  There  is,  however,  no  fib- 
rin in  blood,  but  a  substance  called  fibrinogen. 
The  theory  at  present  in  vogue  is  that  when 


THE  BLOOD  117 

blood  is  shed  there  is  at  once  the  death  of 
many  colourless  cells.  These  contain  a  pro- 
tein called  pro-thrombin,  which,  in  turn, 
produces  an  enzyme  known  as  thrombin,  and 
this  ferment,  in  association  with  salts  of  lime, 
converts  fibrinogen  into  fibrin.  To  account 
for  the  fact  that  blood  rarely  clots  in  living 
vessels,  we  may  assume  the  existence  of  a 
body  produced  by  the  living  cells  lining  the 
vessels  which  prevents  thrombin  from  acting 
(an  anti- thrombin).  There  is  still  uncertainty 
as  to  what  precisely  happens  in  the  remark- 
able phenomenon  of  the  clotting  of  blood, 
and  there  is  little  doubt  that  if  it  were 
thoroughly  understood,  light  would  be  thrown 
on  other  physiological  phenomena,  as  it  may 
be  taken  as  the  type  of  a  certain  class  of 
changes  in  living  matter. 

60.  The  blood  is  not  only  a  nutritional 
medium  but  it  is  also  intimately  connected 
with  respiration.  The  red  cells,  by  the  action 
of  the  pigment  they  contain,  known  as 
haemoglobin,  are  engaged  in  carrying  oxygen 
to  the  tissues  and  also  it  would  appear  to 
some  extent  in  the  carrying  of  carbonic  acid 


118   PRINCIPLES   OF  PHYSIOLOGY 

from  the  tissues  to  the  lungs,  there   to  be 
eliminated. 

61.  In  order  that  the  blood  may  be 
brought  into  close  proximity  to  the  tissues, 
we  find  a  system  of  tubes,  the  organs  of  the 
circulation,  known  as  arteries,  capillaries,  and 
veins,  and  at  one  point  of  the  circulation, 
where  the  arteries  begin  and  the  veins  ter- 
minate, we  find  a  contractile  force-pump,  the 
heart  The  walls  of  the  arteries  near  the  heart 
are  thick,  strong,  and  highly  elastic  ;  in  those 
farther  away  we  find  the  elastic  wall  gradually 
becoming  thinner,  and  a  contractile  wall  of 
non-striated  muscle  appears,  and  becomes 
thicker  as  we  pass  onwards,  until  in  the  smaller 
arteries,  or  arterioles,  the  muscular  coat  is 
the  most  pronounced.  The  arteries  terminate 
in  the  capillaries,  which  form  a  network  of 
minute  tubes,  many  having  a  diameter  of  not 
more  than  the  three-thousandth  of  an  inch. 
These  capillary  networks  bring  the  blood 
close  to  the  living  tissue  elements.  Some 
tissues,  and  always  those  in  which  there  is 
great  physiological  activity,  are  more  vascular 
than  others.  The  capillaries  terminate  in  the 


THE  BLOOD  119 

veins,  thin  walled  vessels,  which  carry  the 
blood  back  to  the  heart.  The  smaller  veins, 
by  their  confluence,  form  larger  and  larger 
veins,  and  the  large  veins,  in  various  situations, 
are  furnished  with  valves  which,  when  open, 
are  directed  towards  the  heart,  and  thus  direct 
the  flow  of  blood  to  that  organ.  The  heart 
itself,  in  man,  has  four  cavities,  two  auricles, 
a  right  and  left,  that  receive  blood,  and 
two  ventricles,  right  and  left,  that  drive 
the  blood  out.  The  right  auricle  receives 
the  blood  from  the  peripheral  parts  of  the 
body,  and  the  left  receives  it  from  the 
lungs.  The  two  auricles  contract  simul- 
taneously. The  two  ventricles  then  simul- 
taneously contract,  the  right  driving  the 
blood  through  the  pulmonary  circulation — 
arteries,  pulmonary  capillaries,  veins — to  the 
lungs,  for  respiratory  purposes,  while  the  left 
ventricle  drives  the  blood  through  the 
systemic  circulation, — arteries,  capillaries,  and 
veins, — through  the  body,  so  as  to  bring  the 
highly  oxygenated  and  nutritious  blood  to 
the  tissues.  Valves  are  placed  at  various 
orifices  of  the  heart  and  they  so  work 


120    PRINCIPLES   OF  PHYSIOLOGY 

that  the  blood   must    flow  in   the   required 
direction. 

62.  The  hydraulic  principles  of  the  circu- 
lation are  remarkable.  Blood  must  flow  from 
situations  of  higher  pressure  to  situations  of 
lower  pressure.  High  pressure  is  kept  up  in 
the  great  arteries  by  the  contractile  action  of 
the  left  ventricle  of  the  heart  acting  like  a 
force  pump  and,  with  each  stroke  of  contrac- 
tion, throwing  blood  into  them,  so  that,  in  a 
sense,  they  are  over-distended.  During  the 
intervals  between  the  heart  beats,  the  walls 
of  the  arteries  recover  themselves  by  the 
resiliency  of  their  elastic  coats.  This  disten- 
sion and  elastic  recoil  constitutes  the  pulse, 
which  is  a  wave  of  motion  along  the  walls  of 
the  arteries,  starting  from  the  heart,  travel- 
ling onwards  with  a  certain  velocity,  and 
becoming  smaller  and  smaller  until  there  is 
no  pulse  in  the  smallest  vessels,  the  capil- 
laries. In  consequence  also  of  the  loss  of 
energy  by  friction,  and  by  the  distension  of 
the  arterial  coats,  the  movement  of  the  blood 
becomes  slower  and  slower  until,  in  the  capil- 
laries, the  blood  is  slowly  meandering  onwards 


THE  BLOOD  121 

at  a  very  low  pressure.  This  is  exactly  the 
condition  most  favourable  for  the  transuda- 
tion  of  fluid  through  the  thin  walls  of  the 
capillaries  for  the  nourishment  of  the  living 
tissues.  But  there  is  another  remarkable 
arrangement  that  suits  two  purposes  :  the 
muscular  wralls  of  the  arterioles,  by  contracting, 
can  vary  the  diameter  of  these  small  vessels. 
When  the  calibre  is  diminished,  it  will  be 
evident  that  the  blood  will  not  pass  through 
the  small  vessels  so  easily  as  it  will  do  when 
the  calibre  is  increased.  The  contractile 
arterioles  act  like  a  kind  of  stop-cock  at  one 
part  of  the  system.  When  the  stop-cock  is 
open,  as  when  the  arterioles  are  dilated, 
the  blood  flows  through  easily,  the  arterial 
system  empties  quickly  through  the  capillaries 
into  the  veins,  and  the  pressure  in  the  greater 
arteries  falls.  When  the  stop-cock  is  partly 
closed,  the  blood  will  meet  with  resistance, 
and  the  pressure  in  the  larger  arteries  rises. 
Thus,  as  the  arterioles  are  always  partially 
contracted  under  the  influence  of  special 
nerves,  there  is  always  a  sufficiently  high 
pressure  in  the  arterial  system  to  keep  up  the 


122   PRINCIPLES   OF  PHYSIOLOGY 

supply  of  blood  to  the  capillary  districts  even 
between  the  heart  beats.  When  the  heart 
ceases  to  beat,  as  at  death,  the  arterioles 
become  at  the  same  time  widely  dilated,  the 
pulse  disappears,  and  by  the  elastic  recoil  of 
the  walls  of  the  great  arteries  the  blood 
passes  through  the  capillaries  into  the  veins. 
Hence,  after  death,  in  ordinary  circumstances, 
the  blood  is  found  in  the  veins,  while  the 
heart  and  arteries  are  empty  It  will  be 
seen,  also,  that  the  contractile  coat  of  the 
arteries  regulates  the  supply  of  blood  to  various 
capillary  districts,  according  to  their  physio- 
logical necessities. 

63.  The  movements  of  respiration  also 
assist  the  circulation.  During  inspiration, 
when  the  chest  is  dilated,  pressure  is  removed 
from  the  surface  of  the  heart  and  of  the  great 
vessels  springing  from  it ;  these  tend  to  dilate 
and  thus  the  blood  is  as  it  were  sucked  towards 
the  heart  by  the  great  veins  and  by  the 
right  auricle  and  right  ventricle.  During 
expiration  there  is  increased  pressure  on  the 
heart,  more  especially  when  expiration  is 
forced,  and  the  blood  does  not  flow  towards 


THE   BLOOD  123 

the  heart  so  easily.  The  flow  of  blood 
towards  the  heart  is  also  favoured  by  muscular 
movements  in  the  limbs  pressing  on  the  thin 
walled  veins,  and  as  these  are  provided  with 
valves  opening  towards  the  heart,  the  blood 
must  flow  onwards.  Pressure  on  the  veins 
of  the  organs  in  the  abdomen  must  also  assist, 
and  so  great  is  the  capacity  of  the  circulatory 
system  in  the  abdominal  and  pelvic  cavities 
that  a  quantity  of  blood  equal  to  all  the  blood 
in  the  body  might  be  therein  contained.  If 
there  is  more  blood  in  one  part  of  the  body 
there  will  be  less  in  another.  An  adjustment 
of  local  circulations  is  constantly  going  on, 
according  to  the  degree  of  physiological 
activity  of  one  organ  or  another.  If  there  is 
a  large  supply  of  blood  to  the  abdominal 
viscera,  as  during  digestion,  or  to  the  skin, 
as  when  exposed  to  heat,  there  will  be  less 
blood  in  other  internal  organs.  This  may  in 
part  account  for  the  mental  lethargy  after  a 
full  meal,  and  for  the  lassitude  one  feels 
during  hot  weather. 

64.  The   circulation   of  the   blood   is   thus 
carried  on  in  accordance  with  the  physical  laws 


124  PRINCIPLES   OF  PHYSIOLOGY 

of  hydraulics.  We  might  imitate  it  roughly 
by  elastic  tubes  and  a  force  pump.  We  can 
drive  water  through  the  streets  and  houses 
of  a  town  by  a  head  of  water  or  a  powerful 
engine,  but  even  with  our  present  technical 
skill,  we  could  not  automatically  regulate  the 
supply  according  to  the  wants  of  different 
districts  by  using  automatically  working 
elastic  and  contractile  pipes. 


CHAPTER  IX 

THE  OUTPUT  OF  WASTE  MATTER 

65.  IT  has  already  been  pointed  out  that  the 
activities  of  the  living  tissues  cause  to  some 
extent  a  breaking  up  of  living  matter,  and  the 
appearance  of  waste  products.  In  addition 
to  this,  waste  matters  may  arise  from  the 
using  up  by  the  protoplasm  in  cells  of  matters 
previously  stored  up  in  them.  That  is  to 
say,  there  may  be  intracellular  chemical 
changes  excited  by  enzymes  in  stored  matters, 
as  well  as  chemical  changes  involving  the 
protoplasm.  Both  of  these  varieties  of  chemi- 
cal change  may  produce  substances  that  are 
of  no  further  use  in  the  body,  and  may  even 
be  injurious  if  allowed  to  accumulate  in  the 
blood.  '  Such  matters  are  not  allowed  to 
accumulate :  they  are  quickly  removed  so 
that  only  small  percentages  are  usually  found 
in  the  blood,  and  this  fluid,  as  has  already 
125 


126   PRINCIPLES   OF   PHYSIOLOGY 

been  explained,  is  maintained  in  a  state  of 
nutritive  equilibrium.  The  separation  and 
elimination  of  waste  matters  are  effected  by 
the  process  termed  excretion.  A  secretion, 
such  as  saliva,  or  gastric  juice,  is  a  fluid 
holding  matters  in  solution  which  have  been 
formed  by  the  activities  of  the  cells  in  secreting 
glands,  and  it  is  intended  to  be  used  for  some 
other  purpose  in  the  economy  of  the  living 
body.  Reference  has  already  been  made  to 
the  uses  of  the  saliva  and  of  the  gastric  juice. 
An  excretion,  on  the  other  hand,  is  the  separa- 
tion from  the  body  of  such  a  fluid  as  urine 
by  the  kidneys,  or  bile  by  the  liver-fluids  of 
no  further  use.  The  chief  excretive  mechan- 
isms will  now  be  considered. 

66.  Lungs.  By  the  process  of  respiration, 
carbonic  acid  is  excreted  by  the  lungs.  This 
substance,  carbonic  acid,  is  produced  in 
connection  with  the  activities  of  all  living 
matter.  It  is  formed  in  the  tissues,  especi- 
ally in  the  glandular,  nervous  and  muscular 
tissues  ;  it  is  abundant  in  lymph  ;  it  exists 
in  the  blood  in  a  state  of  loose  chemico-physi- 
cal  combination  with  the  potassium  salts  and 


OUTPUT  OF  WASTE  MATTER  127 

with  the  haemoglobin  of  the  red  cells.  The 
lymph  surrounding  the  living  tissues  is,  as 
already  explained,  a  respiratory  as  well  as  a 
nutritive  medium.  The  living  elements,  in  a 
sense,  breathe  in  the  lymph.  They  receive 
oxygen  from  it  and  they  give  up  oxygen  to  it. 
The  tension  of  the  oxygen  in  lymph  is  high, 
whereas  that  of  carbonic  acid  is  low,  as  it 
is  quickly  removed.  This  facilitates  the 
interchange  of  gases,  which  we  may  regard 
as  an  internal  respiration.  The  lymph  ulti- 
mately reaches  the  blood  and  carries  the 
carbonic  acid  with  it.  Further,  in  the  tissues 
themselves  there  is  an  absorption  of  carbonic 
acid  by  the  small  capillaries  and  veins.  The 
blood  thus  becomes  venous.  It  is  carried 
away  to  the  right  side  of  the  heart  by  the 
veins,  from  thence  it  passes  by  the  pulmonary 
circulation  to  the  lungs,  and  there  the  carbonic 
acid  is  got  rid  of  into  the  air  cells  of  the  lungs, 
and,  finally,  it  reaches  the  outer  air  in  the 
air  of  expiration.  How  the  carbonic  acid 
passes  out  of  the  capillaries  into  the  air  cells 
has  not  yet  been  clearly  made  out.  The 
tension  of  the  carbonic  acid  in  venous  blood  is 


128   PRINCIPLES  OF  PHYSIOLOGY 

greater  than  the  tension  of  the  gas  in  the  air 
cells  of  the  lung,  and  it  may  be  supposed  that 
this  tension  would  drive  off  the  carbonic  acid. 
Still  there  are  difficulties  with  regard  to  this 
purely  physical  explanation,  and  it  may  be 
that  the  cells  found  on  the  delicate  wall 
between  the  blood  and  the  air  may  exert 
selective  action,  and,  in  a  manner  analo- 
gous to  true  secretion,  excrete  the  carbonic 
acid. 

67.  Respiration,  however,  is  a  double 
function.  Not  only  is  carbonic  acid  eliminated 
in  the  air  cells  of  the  lung,  but  oxygen  is 
absorbed  into  the  blood,  and  by  the  blood 
it  is  carried  to  the  tissues.  There  can  be  no 
doubt  the  oxygen  is  taken  up  by  the  all 
important  constituent  of  the  red  cells  called 
haemoglobin.  It  combines  to  form  a  loose 
union  with  this  pigment,  The  red  corpuscles, 
laden  with  oxygen,  are  hurried  to  the  tissues, 
and  there  a  reverse  process  occurs.  The 
oxygen  leaves  the  oxy-haemoglobin  probably 
in  successive  small  quantities,  passes  into 
the  lymph,  and  is  at  once  taken  up  by 
the  living  tissues.  In  the  air  cells  of  the 


OUTPUT  OF  WASTE  MATTER  129 

lung  the  oxygen  passes  through  the  thin 
wall  between  the  blood  and  the  air  possibly 
physically,  inasmuch  as  the  tension  of  the 
oxygen  in  the  air  cells,  especially  at  the 
end  of  an  inspiration,  is  greater  than  the 
tension  of  the  oxygen  in  the  blood, — but  again 
various  considerations  lead  us  to  suppose  that 
the  taking  up  of  oxygen  may  be  a  vital 
process  due  to  the  activity  of  the  cells  lining 
the  air  cells  and  also  lining  the  vessels.  The 
air  bladder  of  a  fish  is  the  representative  of  the 
lung ;  in  many  cases  it  contains  a  large 
percentage  of  oxygen,  secreted  from  the 
blood  of  the  fish  by  the  epithelium  lining 
the  bladder.  (It  is  remarkable,  however, 
that  in  shallow  water  fishes  the  gas  in  the 
air  bladder  is  chiefly  nitrogen.)  This  oxygen 
was  in  the  first  instance  separated  from  the 
water  by  the  blood  vessels  of  the  gills  as  the 
water  flowed  over  them.  In  the  tissues, 
again,  internal  respiration  may  not  be  entirely 
a  physical  process,  as  we  are  dealing  with 
living  tissues.  Here,  again,  there  may  be 
selection  of  living  gases  by  living  cells. 
What  we  usually  think  of  as  respiration 


180   PRINCIPLES   OF  PHYSIOLOGY 

is  a  series  of  muscular  movements  by  which 
the  chest  expands,  as  in  inspiration,  and 
the  air  rushes  into  the  upper  air  passages 
to  mix  with  the  air  already  there  :  this 
is  followed  in  ordinary  expiration  by  an 
elastic  recoil  of  the  chest  wall  by  which  the 
air  is  expelled  from  the  upper  air  passages. 
The  air  in  those  passages  mixes  with  the  air 
in  the  ultimate  air  cells  by  a  physical  process 
of  diffusion  of  gases.  The  whole  of  this  process, 
the  distension  and  recoil  of  both  chest  wall 
and  lungs,  constitutes  a  pulmonary  ventilation. 
The  essential  phenomena  of  respiration  are, 
however,  in  the  air  cells  and  in  the  tissues. 
The  lungs  may  eliminate  a  small  amount  of 
water  by  evaporation  from  the  respiratory 
gases,  and,  occasionally,  other  matters 
may  pass  off  which  taint  the  breath.  The 
mechanism  of  external  breathing  is  carried 
on  by  a  complex  system  of  muscles  and  by  a 
special  innervation. 

68.  Kidneys.  Excretion  is  also  carried  on 
by  the  kidneys.  These  organs,  which  may  be 
regarded  as  highly  modified  tubular  glands, 
separate  from  the  blood,  water ;  various 


OUTPUT  OF  WASTE  MATTER   131 

saline  matters,  chiefly  chloride  of  sodium 
(common  salt)  and  phosphates  of  the  alkalies 
(potash  and  soda),  and  of  the  alkaline  earths 
(lime  and  magnesia)  ;  various  nitrogenous 
substances,  more  especially  urea,  uric  acid, 
creatinin,  etc.  ;  and  pigmentary  matter. 
The  kidneys  also  take  a  slight  part  in  the 
elimination  of  carbonic  acid.  These  matters 
are  separated  from  the  blood  mainly  by  the 
activity  of  the  epithelial  cells  lining  the 
uriniferous  tubules.  In  the  cortical  part  of 
the  kidney  there  are  remarkable  structures 
known  as  the  Malpighian  Bodies,  consisting 
of  a  glomerulus  or  ball  formed  by  a  network 
of  capillaries,  surrounded  by  the  dilated  end 
of  a  uriniferous  tubule,  so  as  to  form  a  capsule 
lined  by  a  peculiar  form  of  epithelium.  The 
end  of  the  tubule  is  infolded  over  the  capillary 
nodule  so  that  a  double  wall  surrounds  the 
nodule.  Thus  a  somewhat  complex  membrane 
is  formed  like  a  kind  of  cap,  and  three  layers, 
blended  together,  separate  the  blood  from  the 
urine — namely,  the  wall  of  the  capillaries  and 
a  double  wall  formed  by  the  infolded  end  of 
the  tubule.  This  was  once  supposed  to 


132    PRINCIPLES   OF  PHYSIOLOGY 

orm  a  filtration  apparatus  by  which  the 
watery  constituent  of  the  urine,  holding  salts 
and  other  matters  in  solution,  was  filtered 
from  the  blood  through  the  thin  membrane 

nto  the  end  of  the  tubule  It  would  appear, 
however,  that  the  process  is  not  one  of  simple 
physical  filtration,  but  that  there  is  a  selective 
action  due  to  the  vital  activity  of  the  epithe- 
lium. A  minute  vessel  passes  from  the 
glomerulus  or  ball  of  capillaries,  and  this 
divides  again  into  capillaries  which  ramify 
on  the  first  portion  of  the  uriniferous  tubule. 
The  epithelium  in  this  portion  is  of  a  peculiar 
kind,  and  it  has  been  thought  that  it  has  to 
do  with  the  separation  from  the  blood  of  nitro- 
genous matters.  There  is  still  considerable 
obscurity  as  to  the  precise  mechanism  by 
which  urine  is  formed. 

69.  In  a  healthy  man  about  fifty  ounces  are 
excreted  daily.  Its  colour  is  due  to  a  mixture 
of  pigments,  chiefly  urochrome  and  a  small 
amount  of  urobilin.  The  reaction  to  test-paper 
is  acid,  due  chiefly  to  the  presence  of  the  acid 
phosphate  of  soda.  The  origin  and  destination 
of  the  nitrogenous  constituents  require  special 


OUTPUT  OF  WASTE  MATTER  133 

notice,  more  especially  as  illustrating  the 
modes  of  excretion.  It  is  evident  that 
nitrogenous  waste  matters  should  be  soluble 
so  that  they  may  be  carried  off  in  the  urine 
Urea,  of  which  about  five  hundred  grains  are 
eliminated  daily,  is  readily  soluble  in  water 
It  is  a  carb-amide,  and  is  represented  by  the 
formula  CO(NH2).  It  contains  the  same  ele- 
ments as  cyanate  of  ammonia,  but  it  has  not 
the  same  molecular  structure.  Under  the  influ- 
ence of  various  enzymes,  it  takes  up  water, 
and  is  changed  into  ammonium  carbonate, 
which  gives  the  ammoniacal  odour  to  decom- 
posing urine.  In  such  urine  we  always  have  a 
precipitate  of  phosphates  of  lime,  phosphate  of 
magnesia,  and  the  ammoniaco-magnesian,  or 
triple,  phosphate,  as  these  are  not  soluble  in  an 
alkaline  fluid.  As  already  pointed  out,  a  large 
proportion  if  not  the  whole  of  the  urea  is 
formed  in  the  liver  by  the  splitting  up  of  pro- 
tein matter  that  has  come  from  the  intestine, 
and,  to  be  more  precise,  it  is  formed  from 
amino-acids.  This  is  sometimes  spoken  of  as 
the  exogenous  formation  of  urea.  Along  with 
urea  we  always  find  traces  of  ammonia. 


134   PRINCIPLES   OF  PHYSIOLOGY 

One  of  the  substances  produced  by  the 
decomposition  of  muscle-protoplasm  is  a 
nitrogenous  body  called  creatine.  By  union 
with  the  elements  of  water,  it  splits  into  urea 
and  sarcosine,  showing  a  relationship  to  the 
former  substance,  and  possibly  part  of  it 
may  ultimately  be  converted  into  urea,  as  it 
does  not  appear  normally  in  urine.  A 
closely  allied  substance,  differing  from 
creatine  as  regards  its  formula  by  the  loss 
of  the  elements  of  water,  is  creatinine, 
which  always  exists  in  urine.  It  is  in  all 
probability  formed,  not  from  the  creatine 
of  muscle,  as  was  once  supposed,  but  from 
the  metabolism  of  protein  in  the  liver, 
and  as  it  is  poisonous  it  is  thrown  out  in  the 
urine.  There  is  still  obscurity  on  this  point. 
Another  nitrogenous  waste  product  in  the 
urine  is  uric  acid,  of  which  from  seven  to  ten 
grains  are  separated  daily.  Unlike  urea,  it  is 
highly  insoluble,  but  being  an  acid  it  unites 
with  the  alkalies,  soda  and  potash,  to  form 
urates,  which  are  highly  soluble,  and  in  this 
form  it  is  thrown  out.  If  in  excess,  or  if  there 
is  not  sufficient  base  to  unite  with  it,  uric  acid 


OUTPUT  OF  WASTE   MATTER   135 

may  appear  in  various  crystalline  forms  in 
the  urine,  and  when  this  habitually  occurs, 
various  symptoms  of  illness  may  appear 
which  are  spoken  of  as  gouty  or  rheumatic. 
There  can  be  no  doubt  that  uric  acid  is  derived 
from  the  breaking  down,  not  of  cell-substance, 
but  from  the  oxidation  of  nuclein,  one  of  the 
chief  chemical  substances  in  the  nuclei  of 
cells.  This  shows  that  even  nuclei,  on  which 
the  activity  of  cell-life  so  much  depends,  are 
the  seat  of  metabolic  changes,  and  that 
there  are  processes  of  breaking  down.  It  is 
known  that  nuclein  yields,  during  certain 
chemical  reactions,  a  chain  of  nitrogenous 
bodies,  all  more  or  less  closely  related,  known 
as  the  purine  bases.  These  are  purine, 
hypoxanthin,  xanthin,  adenin,  guanin,  and 
uric  acid.  They  sometimes  appear  in  the 
urine  and  they  abound  in  such  tissues  as 
are  the  seat  of  active  metabolism.  Certain 
foods,  such  as  liver  and  sweetbread,  contain 
these  substances.  These  bases  may  thus  be 
formed  exogenously  from  food  stuffs  or  endo- 
genously  by  the  metabolism  of  tissue.  Any 
increased  activity  in  nuclei,  implying  tear 


136    PRINCIPLES   OF  PHYSIOLOGY 

and  wear,    is   shown  by   the   appearance   of 
these  bodies. 

We  have  only  recently  had  a  glimpse  into 
the  transformations  by  which  members  of 
this  series,  ending  in  uric  acid,  are  formed. 
This  is  done  by  the  activity  of  various  enzymes 
found  in  the  tissues.  These  have  been 
extracted  and  their  chemical  activities  studied, 
.and  there  can  be  little  doubt  that  each  of  these 
nucleo-zymases  takes  its  share  in  the  work. 
Some  may  bring  oxygen  into  play  (oxidases), 
while  others  effect  specific  chemical  changes. 
It  would  seem  that  in  the  liver  there  also 
may  be  an  enzyme  which  breaks  up  uric  acid 
itself.  The  ultimate  result  of  these  remark- 
able changes  is  that  substances  arising  from 
the  breaking  up  of  nuclei  are  gradually  trans- 
formed into  uric  acid,  which  (as  urates)  is 
-eliminated  in  a  soluble  form.  Finally,  a 
substance  known  as  hippuric  acid  is  elim- 
inated in  small  amounts  in  the  urine.  It 
abounds  in  the  urine  of  herbivora,  arising  from 
substances  in  the  food  of  such  animals,  and  be- 
longing to  the  benzoic  acid  series.  If  benzoic 
acid  is  given  to  a  man,  it  unites  with  glycine 


OUTPUT  OF   WASTE   MATTER   137 

in  the  liver,  with  the  separation  of  the 
elements  of  water;  hippuric  acid  is  thus 
ormed  and  appears  in  the  urine.  This  is  a 
striking  example  of  a  synthesis  in  the  living 
body. 

70.  Another  organ  by  which  excretion  is 
effected  is  the  skin  This  structure  not  only 
has  a  protective  function,  as  it  covers  the 
whole  surface  of  the  body,  but  it  has  also  an 
excretory  function.  Carbonic  acid  is  to  a 
small  extent  eliminated.  The  sweat,  consist- 
ing of  water  holding  a  small  amount  of  salts 
in  solution  (chiefly  chloride  of  sodium,  and 
phosphates),  is  separated  by  numerous  long 
tubular  glands,  the  sweat  or  sudoriparous 
glands,  lined  with  epithelium.  This  fluid,  at 
certain  temperatures,  may  at  once  pass  into 
a  state  of  vapour  or  gas,  thus  taking  up  heat, 
and  cooling  the  surface,  or,  as  in  profuse 
sweating,  it  may  appear  as  sensible  drops  on 
the  surface  of  the  skin.  A  kind  of  oily 
matter  is  secreted  by  another  set  of  glands 
in  the  skin,  the  sebaceous  glands,  which  some- 
times open  by  ducts  on  the  surface,  or  into  the 
little  pouches  from  which  hairs  spring. 


138   PRINCIPLES   OF  PHYSIOLOGY 

Sebaceous  matter  contains,  in  addition  to 
water  and  a  very  small  amount  of  salts, 
various  fatty  acid  substances.  The  sebaceous 
matter  lubricates  the  surface  of  the  skin. 
The  skin,  however,  has  other  important 
functions.  It  is  not  only  the  organ  by  which 
variations  of  temperature  are  experienced, 
but  it  has  to  do  with  the  regulation  of  the 
temperature  of  the  body.  This  will  be  noted 
in  connection  with  animal  heat.  It  is  also 
the  seat  of  various  sensory  mechanisms  con- 
nected with  the  sense  of  touch. 

71.  Matters  are  also  excreted  from  the 
body  by  the  bowel.  These  consist  of  the 
refuse  materials  of  food  which  have  never 
really  entered  the  tissues  of  the  body,  and 
which  are  therefore  not  true  excretions. 
Along  with  these  there  are  bodies  derived 
from  the  bile,  such  as  pigments,  etc.,  and 
the  secretions  of  the  numerous  mucous  glands 
found  throughout  the  whole  length  of  the 
bowel,  and  more  especially  in  the  great 
bowel.  Little  is  known  of  the  chemical 
nature  of  those  matters,  nor  of  the  exact 
origin  of  the  large  amount  of  saline 


OUTPUT  OF  WASTE  MATTER   139 

matters,  chiefly  phosphates,  found  in  the 
faeces.  Finally  a  large  portion  of  dried 
faecal  matters  consists  of  bacteria,  which 
have  already  been  referred  to  as  existing 
in  enormous  numbers  in  the  alimentary 
canal. 

72.  There  is  still  another  organ  which,  from 
one  point  of  view,  may  be  regarded  as  excre- 
tory, namely  the  liver.     A  portion  of  the  bile 
is  undoubtedly  thrown  out  in  the  faeces,  but 
others  matters  are  re-absorbed  and  return  to 
the  liver.     This  organ  is  the  seat  of  numerous 
chemical  and  vital  processes  that  are  in  a 
sense   hidden.     These  will    be   further   con- 
sidered. 

73.  The  bile  is  an  alkaline  fluid  containing 
usually  a  large  amount  of  a  mucus-like  matter, 
which  gives  it  a  peculiar  "  ropy  "  character 
when  poured  from  one  vessel  into  another.     It 
contains  two  nitrogenous  pigments,  bilirubin 
and    biliverdin.     In    the    bowel    bilirubin    is 
robbed  of  oxygen  by  reduction  processes  and 
becomes  the  pigment  of  the  faeces,  stercobilin. 
Part  of  the  latter  may  be  re-absorbed,  and  is 
then  eliminated  in  the  urine  as  urobilin,  one 


140   PRINCIPLES   OF  PHYSIOLOGY 

of  the  pigments  of  the  urine.  The  origin  of 
these  pigments  is  undoubtedly  the  decom- 
position of  the  haemoglobin  of  effete  or 
worn  out  red  blood  corpuscles.  Where  the 
haemoglobin  is  set  free  and  decomposed  is 
doubtful.  This  probably  occurs  both  in  the 
spleen  and  in  the  liver.  It  is  important  to 
note  that  all  the  blood  that  has  passed  through 
the  spleen  goes  to  the  liver.  The  relation  of 
bilirubin  to  the  blood  pigment  is  undoubted, 
as  haemoglobin  is  a  compound  of  haema- 
tin,  containing  the  all-important  iron,  and  a 
globulin.  If  the  iron  is  removed  from  haematin 
we  have  a  body  called  haematoidin,  or  iron-free 
haematin,  produced.  This  is  identical  with 
bilirubin.  Thus  we  see  the  steps  of  the  pro- 
cess for  the  elimination  of  waste  pigmentary 
matters 

74.  The  bile  contains  the  sodium  salts  of 
highly  complicated  acids,  known  as  the 
bile  acids,  forming  glycocholate  and  tauro- 
cholate  of  sodium.  The  first  is  the  more 
abundant  in  human  bile.  Both  contain 
nitrogen ;  taurocholic  acid  alone  contains 
sulphur.  Each  may  be  split  up  into  (a)  an 


OUTPUT  OF  WASTE   MATTER   141 

acid,  cholalic  acid,  associated  with  glycin  in 
glycocholic  and  with  taurin  in  taurocholie 
acid.  Both  the  origin  and  the  ultimate  fate 
of  the  bile  salts  are  in  obscurity.  As  they  both 
contain  nitrogen,  and  one  contains  sulphur, 
we  must  look  for  their  origin  in  protein 
metabolism,  but  we  know  nothing  of  the  steps 
of  the  process.  In  the  bile  (in  human  bile 
glycocholate  of  soda  forms  the  chief  part  of 
the  solids)  they  reach  the  intestine.  We  are 
not  aware  of  any  special  function  fulfilled  by 
them  in  connection  with  either  intestinal 
digestion  or  intestinal  absorption.  Only  a 
very  small  amount  of  the  bile  salts  appears 
in  the  faeces.  It  follows  that  they  must  be 
re-absorbed  and  carried  back  to  the  liver  by 
the  portal  circulation  and  again  eliminated 
in  the  bile.  Thus  a  kind  of  bile-salt  circula- 
tion has  been  imagined,  but  there  is  no  hint 
as  to  any  use  of  this  arrangement.  Traces 
of  substances  may  appear  in  the  urine  that 
may  have  originated  from  chemical  changes 
in  the  bile  salts.  Lastly,  small  quantities  of 
cholesterin  or  cholesterol  may  be  found  in  bile. 
It  forms  the  chief  constituent  of  gall-stones, 


142   PRINCIPLES   OF  PHYSIOLOGY 

concretions  formed  in  the  bile  ducts  and  in  the 
gall  bladder  The  origin  of  this  substance  is 
still  imperfectly  known,  but  it  is  formed  from 
metabolism  of  tissue.  It  is  present  in  all  cells, 
and  when  these  are  broken  down,  it  is  not 
thrown  out  as  a  waste  product,  but  is  used  up 
to  form  new  cells.  Thus,  red  blood  corpuscles 
are  disintegrated  in  the  liver  and  cholesterin 
appears  in  the  bile.  It  is  then  re-absorbed, 
probably  with  other  substances,  and  is  carried 
to  the  tissues  to  form  new  cells.  This  is  a 
striking  example  of  physiological  economy. 

75.  By  those  various  processes  of  excretion 
waste  matters  and  injurious  matters  are 
removed  from  the  blood,  as  has  already  been 
explained.  This  fluid  is  therefore  maintained 
in  a  condition  of  physiological  equilibrium, 
and  this  is  more  remarkable  when  we  consider 
that  it  is  constantly  the  seat  of  exchanges. 
It  is  almost  momentarily  receiving  matters 
on  the  one  hand  and  giving  them  up  on  the 
other.  In  a  sense,  everything  removed  from 
the  blood  must  more  or  less  alter  its  quality. 
From  this  point  of  view  the  growth  and 
development  of  the  epidermic  cells  on  the 


OUTPUT  OF  WASTE   MATTER   143 

surface  of  the  skin,  and  which  are  constantly 
being  shed  from  the  surface  in  myriads,  the 
growth  and  development  of  all  epidermic 
appendages,  such  as  hairs,  nails,  horn,  feathers, 
etc.,  remove  certain  matters  from  the  blood 
and  alter  its  quality.  We  may  indeed  go 
farther  and  say  that  the  development  and 
growth  of  all  tissues,  as  they  depend  on  matters 
taken  from  the  blood,  must  alter  that  fluid 
Thus  we  may  understand  that  the  abnormal 
development  of  any  tissue  or  organ  must  have 
a  similar  effect,  and  in  some  such  way  the 
nutrition  of  one  organ  must  affect  that  of  the 
others. 


CHAPTER   X 

HIDDEN     PROCESSES     AND     ULTIMATE     PHENO- 
MENA  OF   NUTRITION 

76.  THERE  are  not  a  few  processes  occurring 
in  the  body  which  are  so  hidden  as  not  to  be 
at  all  evident  to  a  superficial  examination  ; 
and  yet  they  are  of  the  highest  importance. 
Several  examples  of  these  may  now  be  referred 
to.  First,  we  will  consider  what  is  usually 
called  the  glycogenic  function  of  the  liver. 
This  organ,  the  largest  gland-like  structure  in 
the  body,  consists  of  myriads  of  cells,  the 
hepatic  cells,  and  it  is  more  richly  supplied 
with  capillary  blood  vessels  than  any  other 
structure  in  the  body.  It  receives  two  kinds 
of  blood,  red  arterial  blood  from  the  systemic 
circulation  by  the  hepatic  artery,  and  blood 
more  like  venous  blood,  often  laden  with 
matters  derived  from  the  alimentary  canal — 
portal  blood — by  the  portal  vein.  The  blood, 

144 


HIDDEN   PROCESSES  145 

after  circulating  through  the  liver,  is  carried 
off  by  a  single  vein,  the  hepatic  vein,  which 
pours  it  into  the  systemic  venous  circulation. 
There  it  mixes  with  other  venous  blood, 
reaches  the  right  side  of  the  heart,  passes  to 
the  lungs  (pulmonary  circulation),  is  sent  on  to 
the  left  side  of  the  heart,  and  is  then  propelled 
by  the  systemic  circulation  to  all  parts  of  the 
body.  Thus,  as  already  mentioned,  the  whole 
of  the  blood  that  has  circulated  through  the 
alimentary  canal  passes  through  the  liver 
before  it  reaches  the  general  venous  system. 
This  is  the  portal  circulation.  In  the  cells  o! 
the  liver  very  active  metabolic  changes  take 
place,  new  substances  are  formed,  complex 
bodies  are  split  up,  possibly  red  corpuscles  are 
decomposed,  and  as  the  result  of  all  this,  we 
have  bile  formed,  which,  as  already  seen, 
passes  into  the  first  portion  of  the  small  bowel, 
the  duodenum.  The  formation  of  bile  was  at 
one  time  regarded  as  the  proper  function  of  the 
liver.  But  it  is  now  known  that  this  is  not 
the  case.  The  bile  is  only  a  by-product  led 
off  from  this  remarkable  manufactory. 

77.  As  already  pointed  out,  the  blood  with 


146   PRINCIPLES   OF  PHYSIOLOGY 

which  the  liver  is  supplied  by  the  portal 
system  contains  during  the  digestive  and 
absorptive  processes  large  amounts  of  pro- 
teid  and  of  carbo-hydrate  in  the  form  of 
grape  sugar.  What  happens  to  the  proteid 
has  already  been  discussed  (p.  66).  A  portion 
of  it,  however,  may  be  decomposed  into  a 
nitrogenous  and  a  non-nitrogenous  portion. 
The  nitrogenous  portion  may,  by  synthesis, 
assist  in  the  formation  of  other  molecules  of 
proteid  or  of  certain  bodies  found  in  the  liver, 
such  as  the  complicated  bile  acids  which, 
united  to  soda  to  form  the  bile  salts,  appear  in 
the  bile  (p.  140).  In  the  chemical  changes 
affecting  the  nitrogenous  portion  one  of  the 
bodies  formed  is  undoubtedly  urea  (p.  132). 
This  substance  often  represents  an  excess  of 
proteid  in  the  diet ;  at  all  events  a  meal  rich 
in  proteid  is  followed  by  an  increased  forma- 
tion of  urea.  The  urea  is  washed  out  of  the 
liver  by  the  blood,  but  as  it  is  quickly  removed 
by  the  kidneys,  it  appears  in  the  urine,  and 
the  percentage  amount  in  the  blood  is  always 
small.  On  the  other  hand,  the  non-nitro- 
genous residue  of  the  proteid  may  apparently 


HIDDEN   PROCESSES  U7 

be  transformed  into  a  carbo-hydrate,  and  it 
may  be  one  of  the  sources  of  the  distinguishing 
carbo-hydrate  in  the  liver  known  as  glycogen. 
78.  The  chief  source  of  glycogen,  however, 
is  undoubtedly  grape  sugar  that  has  arrived 
in  the  portal  blood  from  the  alimentary 
canal.  Glycogen  is  a  non-nitrogenous  body 
much  resembling  starch,  indeed  it  may  be 
regarded  as  an  animal  starch.  After  a  period 
of  digestion  and  absorption,  it  is  found  in 
the  form  of  minute  granules  in  the  interior 
of  many  hepatic  cells.  For  a  time  it  is  stored 
in  these  cells,  so  that  the  liver  is  a  storehouse 
of  carbo-hydrate.  It  is  interesting  to  note 
that  in  digestion,  as  we  have  seen,  all 
carbo-hydrate  is  transformed  into  grape  sugar, 
while  in  the  liver  we  find  the  process  reversed 
and  a  kind  of  starch,  glycogen,  is  again  formed 
from  grape  sugar.  The  first  transformation 
is  accomplished  by  various  enzymes,  while  the 
second  is  effected  by  the  living  hepatic  cells, 
or  possibly  by  an  enzyme  in  the  cells  While 
absorption  is  going  on,  a  certain  amount  of 
grape  sugar  passes  through  the  liver  un- 
changed, and  is  carried  to  the  muscles,  where 


148   PRINCIPLES   OF  PHYSIOLOGY 

it  is  used  up  in  the  chemical  processes  occur- 
ring in  that  tissue  connected  with  contraction. 
During  the  intervals  between  absorptive 
periods,  and  while  no  carbo-hydrate  is  derived 
from  the  bowel,  the  muscles  still  require 
carbo-hydrate,  and  this  they  obtain  from  the 
store  of  glycogen  stored  in  the  hepatic  cells. 
How  the  glycogen  is  removed  from  the  cells, 
and  again  re-transformed  into  sugar,  either 
in  the  hepatic  cells,  or  in  the  colourless  cor- 
puscles, or  in  the  muscular  tissues  themselves, 
has  not  yet  been  clearly  explained.  Probably 
again  enzyme  action  is  called  into  play. 
Another  enzyme  has  been  found  in  the  liver, 
capable  of  transforming  the  glycogen  into 
sugar,  and  various  sugar-forming  substances 
have  been  found  in  muscle.  There  appears  to 
be  in  muscle,  especially  at  an  early  stage 
of  development,  a  variety  of  glycogen,  or 
carbo-hydrate  destined  for  its  nutrition.  The 
phenomena  that  occur  in  the  hepatic  cell 
are  unknown.  It  is  possible,  as  already  sug- 
gested, that  the  transformations  in  protein 
matter,  as  well  as  in  carbo-hydrate  matter, 
may  be  one  intricate  chemical  operation — a 


HIDDEN   PROCESSES  149 

series  of  decompositions  succeeded  by  syn- 
theses— one  result  of  which  is  the  throwing 
out  of  useless  residues  that  are  found  in 
some  of  the  constituents  of  the  bile.  The 
glycogenic  function  gives  us  only  a  glimpse 
into  the  nature  of  the  complex  chemical 
phenomena  occurring  in  a  hepatic  cell.  In 
the  liver  also  there  appears  to  be  a  destruction 
of  effete  red  blood  corpuscles  with  the  decom- 
position of  haemoglobin,  and  the  excretion  in 
the  bile  of  pigments  and  of  cholesterol. 

79.  In  recent  years  a  remarkable  discovery 
has  been  made  with  regard  to  certain  organs 
that  were  previously  a  puzzle  to  physiologists, 
such  organs  as  the  thyroid  body  or  gland 
found  in  front  of  the  upper  end  of  the  trachea 
or  windpipe ;  the  two  suprarenal  bodies  found 
immediately  above  the  upper  end  of  each 
kidney ;  the  pituitary  body  found  at  the  base  of 
the  brain ;  the  spleen,  lying  on  the  left  side  of 
the  stomach ;  and  various  organs  now  known 
to  belong  to  the  lymphatic  system,  such  as 
the  lymphatic  glands,  the  tonsils,  and  the 
Peyerian  glands  found  in  the  small  intestine, 
more  especially  in  its  third  and  lower  portion, 


150   PRINCIPLES   OF  PHYSIOLOGY 

the  ileum.  These  organs  all  agree  anatomi- 
cally in  having  no  duct  Hence,  they  are 
sometimes  called  the  ductless  glands.  It  is  a 
misnomer  to  call  them  glands,  as  they  are  not 
in  any  sense  true  glands,  and  they  would  be 
more  aptly  designated  "  body  "  or  "  bodies." 
All  those  organs  that  belong  to  the  lymphatic 
system  proper  contain  a  peculiar  kind  of 
tissue,  known  as  lymphoid  tissue  (found  also 
in  the  marrow  of  bone  and  below  mucous 
surfaces),  consisting  of  a  network  of  fine 
fibres,  with  small  masses  of  protoplasm  at  the 
junctions  of  the  fibres,  as  if  the  tissue  were 
formed  of  star-shaped  cells,  the  rays  of  which 
unite  or  anastomose  to  form  a  network.  These 
lymphatic  bodies  are  concerned  in  the  develop- 
ment and  growth  of  colourless  cells  of  the 
blood,  but  it  is  probable  they  have  other 
hidden  functions  at  present  unknown. 

80.  The  other  bodies  above  mentioned  are 
now  known  to  form  what  have  been  termed 
internal  secretions,  which  have  important 
physiological  effects.  Thus  the  thyroid  body 
forms  a  chemical  substance,  now  known  as 
thyroidin,  which  contains  iodine,  and  which 


HIDDEN   PROCESSES  151 

seems  to  have  the  property  of  destroying 
mucinoid  material,  probably  absorbed,  in  a 
more  or  less  modified  condition,  from  mucous 
surfaces.  At  all  events  atrophy  of  the  thyroid 
body  produces  a  peculiar  disease  known  as 
myxoedema,  in  which  the  cellular  tissues  are 
infiltrated  with  a  mucinoid  matter,  while  there 
are  symptoms  of  an  anaemia  (deficiency  of  red 
cells  of  the  blood).  This  condition  is  much 
modified  or  disappears  on  administering  raw 
thyroid,  powdered  thyroid,  or  the  thyroidin 
extracted  from  the  organ  of  the  sheep  or 
similar  mammal.  As  curious  nervous  symp- 
toms appear  after  removal  of  the  thyroid  it 
may  have  other  internal  functions. 

81.  The  suprarenal  bodies  were  at  one  time 
thought  to  have  to  do  with  the  formation 
or  modification  of  pigment,  and  possibly  this 
may  be  the  case,  but  they  are  now  known  to 
produce  a  chemical  substance  termed  adrena- 
lin, which  has  a  specific  action  in  stimulating 
non-striated  muscular  fibre.  Thus  it  stimu- 
lates the  coats  of  the  arterioles,  causing 
their  calibre  to  be  very  much  diminished, 
and  as  the  heart  still  vigorously  beats,  the 


152    PRINCIPLES   OF   PHYSIOLOGY 

pressure  of  the  blood  in  the  great  vessels  is 
much  increased,  a  condition,  within  limits, 
favourable  to  a  vigorous  circulation.  Adrena- 
lin is  now  used  medicinally,  as  a  powerful 
styptic  by  which  bleedings  may  be  arrested. 
This  is  a  striking  example  of  a  so-called  internal 
secretion. 

82.  Similarly  the  pituitary  body  appears  to 
exert  an  influence  on  the  growth  and  develop- 
ment of  bone,  and  morbid  conditions  of  the 
organ   are   apparently  related   to   a    curious 
disease  called  acromegaly,  in  which  the  bones 
of  the  face  and  fingers  in  particular  become 
enormously    developed.     This   subject,    how- 
ever, is  still  obscure. 

83.  Another    organ  which  is    the    seat    of 
many  hidden  processes  is  the  spleen.     It  is 
the  largest   of  the   ductless   glands.     It  has 
a  strong   fibrous  capsule,   and  passing  from 
the  capsule  in  all  directions  into  the  interior 
of  the  organ  we  find  septa  or  partitions  of 
connective    tissue    and    unstriated    muscle, 
dividing  the  organ  into  numerous  compart- 
ments.    These   are   filled   with   spleen   pulp. 
This  pulp  consists  of   finer  fibres  forming  a 


HIDDEN   PROCESSES  153 

kind  of  network,  in  the  meshes  of  which  are 
numerous  granular  corpuscles  like  those  found 
in  lymph.  There  are  also  numerous  red 
corpuscles  and  also  cell-like  bodies  enclosing 
red  corpuscles  or  pigmentary  matter.  The 
splenic  artery  which  brings  blood  to  the  spleen 
divides  into  branches  like  the  twigs  of  a  tree  ; 
there  are  no  capillaries;  the  blood  infiltrates 
the  pulp  ;  and  from  the  spaces  in  which  the 
pulp  lies  veins  originate  which,  by  confluence, 
form  the  splenic  vein.  The  blood  of  the  splenic 
vein,  as  already  mentioned,  passes  to  the 
liver  (p.  140).  The  spleen  has  also  curious  little 
masses  of  lymphoid  tissue,  called  Malpighian 
corpuscles,  which  are  closely  connected  with 
the  branching  vessels.  The  chief  function  of 
the  spleen  is  the  formation  of  colourless  blood 
corpuscles,  especially  by  the  lymphoid  tissue  in 
the  Malpighian  bodies.  The  blood  of  the  splenic 
vein  is  always  rich  in  white  corpuscles.  There 
is  little  doubt  also  that  disintegration  of  effete 
corpuscles  occurs  in  the  spleen,  and  from 
these  chemical  substances  are  formed  like 
those  originating  in  nitrogenous  metabolism, 
such  as  those  of  the  uric  acid  series  (p.  135). 


154    PRINCIPLES   OF   PHYSIOLOGY 

Curious  rhythmical  movements  of  the  spleen 
have  been  studied,  and  on  a  tracing  of  these 
movements  large  waves  occur  about  once  in  a 
minute ;  on  these  there  are  smaller  waves  due 
to  respiratory  movements ;  and  on  these,  again, 
still  smaller  waves,  corresponding  to  the  beats 
of  the  heart.  This  rhythmic  mechanism 
must  assist  in  the  transmission  of  blood 
through  the  organ.  It  is  influenced  by  special 
nerves. 

84.  The  ihymus  gland,  found  in  the  chest 
behind  the  breastbone,  is  a  blood  gland  of 
later   foetal    and    early   infantile  life.     Very 
little  is  known  of  its  functions. 

85.  It    is    suspected    that    other    organs, 
having  definite  functions  with  which  we  are 
acquainted,  have  also  hidden  functions  little 
understood.     In  this  way  the  kidneys  may 
have  a  hidden  function ;  at  all  events  removal 
of  a  kidney,  or  even  a  portion,  has  been  found 
to  affect  the  general  nutrition  of  the  body. 
In  some  similar  way  the  generative  organs, 
ovary    and    testis,    especially    during    their 
development,  may  influence  the  nutrition  of 
other  parts.     This  is  seen  to  a  marked  degree 


HIDDEN   PROCESSES  155 

in  many  animals,  more  especially  in  birds  in 
the  growth  of  epidermic  appendages,  such  as 
the  wattles  of  the  male  turkey,  or  the  horns  of 
the  stag.  In  man  also,  when  puberty  is  reached , 
there  are  changes  in  the  general  nutrition  of 
the  female  and  in  the  appearance  of  the  beard 
in  the  male.  Such  phenomena  have  been 
termed  those  of  complemental  nutrition,  a 
term  of  little  meaning  unless  we  associate  with 
it  the  conception  that  the  nutrition  of  such 
organs  in  some  way  affects  the  quality  of  the 
blood,  possibly  by  an  internal  secretion,  and 
that  this  altered  quality  affects  the  nutrition 
of  other  organs. 

86  We  have  now  to  approach  what  is 
known  regarding  the  processes  in  the  living 
cell  on  which  the  ultimate  phenomena  of 
nutrition  depend.  Each  cell,  as  we  have  seen, 
is  bathed  by  lymph  which  has  been  furnished 
by  the  blood.  Under  no  circumstances  does 
the  blood  come  into  direct  contact  with  the 
living  tissues  outside  the  vessels.  No  doubt 
the  walls  of  the  vessels  themselves  contain 
living  elements,  and  we  may  regard  the  wall 
of  an  ultimate  capillary  as  alive.  But,  so  far 


156    PRINCIPLES   OF  PHYSIOLOGY 

as  the  outer  tissues  are  concerned,  there  is 
always  the  internal  medium,  the  lymph. 
This  supplies  the  living  cell  with  matters 
prepared,  as  we  have  seen,  by  complicated 
processes,  and  now  fit  for  assimilation.  The 
lymph  also  supplies  the  living  matter  with 
oxygen.  How  they  are  actually  assimilated 
we  do  not  know ;  we  are  now  in  the  most  hidden 
region  of  life.  In  the  cell  we  find  living  proto- 
plasm, and  along  with  it,  in  many  cases, 
probably  in  all  cases  at  some  period  or  other 
of  the  life  of  the  cell,  matters  that  have  been 
stored  up  so  as  to  form  the  elements  of 
secretions,  or  the  substances  necessary  for  the 
vital  activities  of  the  cell. 

As  examples,  takes  the  granules  in  a  secret- 
ing cell  which  has  rested  for  some  time,  or  the 
granules  in  nerve  cells,  after  a  period  of  rest. 
If  we  call  the  protoplasm  a  and  the  stored 
matters  b,  we  do  not  know  whether  b  has  at 
one  time  been  part  of  a,  or  whether  a,  by  some 
hidden  chemistry,  has  made  b  outside  of  its 
own  substance.  But  there  is  also  inter- 
cellular matter,  which  we  may  call  c,  and  which 
has  been  formed  by  a.  Such  inter-cellular 


HIDDEN   PROCESSES  157 

matter  we  see  in  the  matrix  or  ground 
substance  of  cartilage,  the  fibrous  material 
of  osseous  tissue,  and  the  substance  of 
muscular  fibre  outside  the  nuclei.  The  ques- 
tion arises — are  a,  b  and  c  all  alive,  or  are  the 
phenomena  of  life  to  be  limited  to  those 
occurring  in  a,  the  protoplasm  ?  There  can 
be  little  doubt  that  life  must  be  limited  to  the 
protoplasm.  We  can  scarcely  imagine  the 
stored  matter  b  or  the  inter-cellular  matter  c 
to  be  alive.  They  do  not  manifest  the  general 
phenomena  of  living  matter,  although  they 
may  be  and  are  highly  complex  materials. 
This  brings  us  then  to  consider  what  happens 
in  a.  Undoubtedly  there  is  evidence  that 
in  it  there  are  both  anabolic  and  katabolic 
processes,  processes  both  of  breaking  down 
and  of  repair,  as  shown  by  the  appearance 
in  the  lymph  of  chemical  substances  that 
could  not  have  been  derived  from  b  but 
only  from  a.  According  to  this  view,  only 
matter  taken  up  into  a,  assimilated  by  it, 
becomes  alive,  but  it  is  doubtful  if  even 
here  we  can  draw  a  dividing  line  between 
what  is  living  and  what  is  dead.  We  forget 


158    PRINCIPLES   OF  PHYSIOLOGY 

that  we  may  here  be  in  a  region  where  there 
are  no  sudden  jumps  but  transitional  processes. 
Even  when  matter  has  been  taken  up  by 
the  living  epithelium  of  the  alimentary 
canal,  it  has  been  altered.  Thus  protein 
matters,  as  we  have  seen,  are  split  up  ulti- 
mately to  form  bodies  known  as  amino-acids ; 
these,  in  passing  through  the  living  epithelial 
cells,  are  synthetized  into  serum  albumen  or 
other  blood  proteins ;  these  again  are  probably 
modified  in  the  protoplasm  of  lymphoid  tissue 
and  in  lymphatic  bodies ;  and  ultimately  the 
protein  matter,  no  longer  like  the  same  proteim 
that  it  was  at  first,  is  now,  in  the  lymph, 
brought  near  the  living  matter  of  the  cell. 
Here  we  may  assume  that  these  prepared 
proteins  are  linked  on  to  the  living  matter  by 
hidden  chemical  affinities,  and  thus  become 
incorporated  with  it.  There  have  been  no 
sudden  leaps,  but  a  series  of  processes  ;  there 
is  no  sharp  dividing  line  between  what  is  dead 
and  what  is  living.  So-called  dead  matter, 
by  these  processes,  has  acquired  properties 
it  did  not  possess  before  ;  and  so-called  living 
matter  has  by  the  process  that  we  call  nutri- 


HIDDEN   PROCESSES  159 

tion  developed  new  properties  which  we  say 
are  shown  only  by  matter  which  is  alive. 
But  only  living  matter  can  carry  out  these 
transitions.  They  cannot  be  accomplished 
by  either  b  or  c — only  by  a. 

It  is  conceivable  that  it  is  by  purely  physical 
processes  that  matters  are  taken  up  by  the 
living  cell,  so  as  to  reach  the  protoplasm. 
The  thin  layer  of  structureless  matter  lining 
the  wall  of  a  living  cell,  and  indeed,  so  far, 
constituting  the  wall,  may  act  like  a  mem- 
brane used  in  physical  experiments  on  osmo- 
tic action.  It  is  well  known  that  such  a 
membrane  may  allow  certain  substances  to 
pass,  while  it  is  impermeable  to  other  sub- 
stances. The  matters  that  can  pass  through 
are  soluble  in  the  matter  forming  the  mem- 
brane, while  insoluble  substances  are  rejected. 
In  the  living  matter,  the  protoplasm,  we  have 
seen  that  chemical  processes  occur.  But 
physical  chemists  know  that  many  chemical 
processes  are  reversible,  that  is  to  say,  in  the 
first  stage,  from  certain  bodies  (a)  other 
bodies  (b)  are  formed,  and  in  a  second  stage, 
and  under  different  physical  conditions,  (b) 


160    PRINCIPLES   OF  PHYSIOLOGY 

may  again  become  (a)  by  the  chemical 
process  being  reversed.  Such  phenomena 
may  happen  in  a  cell,  and  they  may 
account  for  so-called  anabolic  and  katabolie 
changes. 


CHAPTER    XI 

THE    LIBERATION    OF   ENERGY 

87.  WE  have  already  seen  that  energy  is 
liberated  by  the  splitting  up  of  complex 
into  simpler  substances.  By  liberation  we 
mean  the  setting  free  of  energy  as  kinetic 
energy.  Thus  by  the  explosion  of  gunpowder 
or  of  gun  cotton,  the  mass  is  resolved  into 
gases  at  a  high  temperature,  and  the  expansion 
of  these  gases  is  used  to  drive  a  projectile 
from  a  cannon.  The  energy  of  the  explosive 
is  resolved  into  heat  and  motion.  This  latent 
energy  may  be  set  free  by  communicating  to 
it  the  shock  of  a  hair  trigger,  and  the  amount 
of  energy  of  the  hair  trigger  is  infinitesimally 
small  compared  with  that  set  free  by  the 
explosion.  The  energy  of  the  trigger  may  be 
regarded  as  a  liberator  of  the  energy  in  the 
explosive.  This  analogy  helps  in  understand- 
ing the  phenomena  in  certain  tissues.  Thus 

L  161 


162    PRINCIPLES   OF  PHYSIOLOGY 

in  muscular  tissue,  energy  is  latent  when  the 
muscle  is  at  rest,  but  when  the  nervous  impulse 
reaches  it  by  travelling  in  a  nerve  the  muscle 
contracts,  becomes  warmer  and  does  work  by 
motion,  in  one  form  or  another.  The  nervous 
impulse  is  the  liberator, — the  muscle  substance, 
along  with  the  chemical  phenomena  we  have 
considered,  liberates  energy  as  heat  and  motion. 
In  like  manner,  energy  is  stored  up  in  all 
living  matter,  in  the  secreting  cell,  in  the  tissues 
of  the  nervous  system,  and  probably  in  other 
living  tissues,  and  it  is  set  free  by  a  nervous 
impulse.  This  explains  why  heat  is  developed 
in  a  secreting  gland  during  its  activity,  and 
if  we  had  adequate  experimental  appliances, 
we  should  find  evidence  of  heat  in  all  vital 
activities. 

88.  Heat  is  also  produced  in  the  body  in 
other  ways.  The  friction  of  the  blood  on  the 
walls  of  the  vessels  as  it  is  driven  along  in  the 
circulation  is  resolved  into  heat,  in  other 
words  all  the  energy  of  the  circulation  becomes 
heat.  In  like  manner  the  movements  of 
organs  causing  friction  produce  heat.  But 
the  great  sources  of  heat  are  the  phenomena 


THE  LIBERATION  OF  ENERGY    163 

that  occur  in  muscle  and  in  secreting  glands, 
The  amount  of  heat  produced  in  other  ways  is 
comparatively  small.  The  body  may  also 
receive  heat  by  the  ingestion  of  hot  food  or 
drink  and  by  conduction  and  radiation  from 
the  surrounding  medium.  The  amount  of 
heat  thus  produced  in  a  living  body  is  very 
large,  and  if  it  were  not  lost  from  the  body  in 
in  some  way,  the  mean  temperature  of  the 
body  would  soon  rise  to  a  degree  incompatible 
with  life.  But  the  arrangements  for  the 
removal  of  heat  are  efficient.  It  is  thrown 
off  from  the  body  into  the  surrounding 
medium  by  conduction  and  radiation  if  the 
temperature  of  the  medium  is  below  that  of  the 
mean  temperature  of  the  body.  Heat  is  lost 
by,  in  some  circumstances,  taking  cold  food 
or  drink,  or  by  the  evacuations.  It  is  also 
lost  by  becoming  latent  in  the  evaporation  of 
sweat  from  the  surface  of  the  skin,  that  is  to 
say  heat  is  lost  in  converting  the  sweat  into 
vapour.  Thus  the  body  is  maintained  in 
normal  circumstances  at  a  mean  temperature 
in  the  armpit  of  98.40°  Fahrenheit. 

89.  If  we  estimated  all  the  heat  entering  the 


164    PRINCIPLES   OF   PHYSIOLOGY 

body  and  added  it  to  that  produced  in  the 
body  itself,  say  in  twenty-four  hours,  it  would 
normally  be  about  equal  to  that  given  off  by 
the  body  in  the  same  time.  The  income  and 
the  expenditure  would  be  about  equal,  and 
the  mean  bodily  temperature  would  be  fairly 
constant.  If  more  heat  were  produced  than 
could  be*  got  rid  of,  as  in  fever,  the  mean 
temperature  would  rise,  whereas  if  less  heat 
was  produced  than  was  given  off  the  mean 
temperature  would  fall.  It  would  appear  that 
vital  activities  can  be  carried  on  efficiently 
only  within  a  narrow  range  of  temperature. 
Hence  the  danger  to  life,  in  many  diseases,  if 
the  temperature  rises  above  104°  or  105°.  A  fall 
of  temperature  ten  or  twelve  degrees  below 
normal  temperature  is  not  so  dangerous.  The 
activity  of  the  skin  in  producing  sweat,  and 
the  evaporation  of  the  sweat,  is  the  great 
regulator.  Hence  there  is  danger  to  life  in 
certain  parts  of  the  tropics  where  there  may  be 
an  air  temperature  above  98°  F.,  and  where  the 
air,  at  that  temperature,  may  be  saturated 
with  aqueous  vapour.  Here  evaporation  from 
the  skin  is  impossible,  heat  penetrates  from 


THE  LIBERATION  OF  ENERGY    165 

without,  and  the  mean   temperature   of   the 
body  must  gradually  rise. 

90.  Energy  is  also  liberated  as  motion  by  the 
contractions  of  the  muscles.  The  muscles  may 
either  perform  internal  work, — as  the  beating 
of  the  heart,  the  movements  of  respiration,  the 
movements  of  the  limbs  on  the  trunk,  the 
movements  of  the  involuntary  muscles,  as  of 
the  bladder  and  bowel, — or  external  work,  as 
in  locomotion  or  in  mechanical  labour.  All 
internal  movement  is  ultimately  resolved 
into  heat.  The  external  work  can  also  be 
measured  and  expressed  as  heat,  and  thus  the 
total  energy  of  the  body  in  twenty-four  hours 
liberated  by  a  man  doing  say  eight  or  ten  hours 
of  hard  work  can  be  calculated.  Further, 
the  energy  represented  by  the  complete  com- 
bustion of  a  diet  sufficient  for  a  man  doing 
this  work  and  producing  heat  during  twenty- 
four  hours  can  also  be  calculated.  It  can  be 
shown  that  there  is  a  balance  struck  between 
income  and  expenditure,  and  this  balance, 
in  ordinary  circumstances,  is  fairly  constant. 
It  becomes  interesting  to  consider  man  as  a 
transformer  of  energy  with  special  reference 


168    PRINCIPLES   OF  PHYSIOLOGY 

to  the  amount  of  energy  he  can  liberate  as 
mechanical  work  and  the  ratio  of  this  amount 
to  the  amount  of  energy  appearing  as  heat. 
The  best  results  show  that  about  25  per  cent, 
of  the  available  energy  appears  as  work,  with 
75  as  heat.  This  compares  favourably  with 
many  human  contrivances.  The  best  steam- 
engine  can  only  give  about  12  J  per  cent,  of 
the  energy  produced  by  complete  combustion 
of  the  fuel,  but  gas  or  petrol  engines  can  do 
much  better — as  much  as  96-98  per  cent,  of 
energy  can  be  transmuted  by  certain  electrical 
contrivances.  The  heat  of  the  engine,  how- 
ever, is  a  real  loss  of  energy,  and  all  engineers 
strive  to  reduce  it  to  a  minimum,  but  the  heat 
of  the  body  is  one  of  the  all-important  conditions 
of  its  mechanism.  The  source  of  error  in  all 
such  estimations  is  that  food  stuffs  are  never 
completely  oxidised  in  the  body,  and  further 
that  the  methods  followed  by  the  engineer  in 
measuring  the  output  of  energy  are  different 
from  those  of  the  physiologist.  Still  the 
general  statement  is  fairly  correct. 

91.  In  some  animals  energy  is  liberated  in  the 
form  of  electrical  energy  or  light,  as  in  the  electric 


THE  LIBERATION  OF  ENERGY    167 

fish  and  the  glow-worm  and  fireflies.  Even 
in  the  human  body  there  are  also  electrical 
phenomena.  Every  contraction  of  a  muscle, 
the  secretion  of  a  gland,  and  probably  also 
nutritional  changes  in  the  tissues,  are  asso- 
ciated with  electrical  phenomena,  which  may 
be  demonstrated  by  a  sensitive  galvanometer 
and  suitable  methods.  It  can  be  shown  that 
antecedent  to  every  muscular  contraction 
there  is  generated  a  change  in  the  electrical 
condition  of  the  muscle.  Whether  this  elec- 
trical state  is  an  expression  of  the  chemical 
changes  in  the  muscle,  on  which  motion  and 
heat  depend,  or  whether  it  is  an  isolated  physi- 
cal phenomenon,  it  is  difficult  to  say.  Even 
the  heart  beats  are  associated  with  electrical 
phenomena.  Living  nerves  also  show  elec- 
trical changes  similar  in  kind  to  those  found 
in  muscle.  It  is  significant  that  the  electrical 
organs  of  fishes  are  modifications  of  muscles 
or  glands.  Thus  the  electrical  organs  of  the 
Torpedo  occellata  (of  the  Mediterranean),  of 
the  Gymnotus  electricus  or  electric  eel  (of  the 
Orinoco),  and  of  the  skates  (Raid)  are  all 
modifications  of  muscle,  while  that  of  the 


168    PRINCIPLES   OF  PHYSIOLOGY 

mud-fish  of  the  Nile,  Malopterurus  electricus, 
is  a  modification  of  glands  of  the  skin. 

92.  Further,  it  would  appear  that  modern 
views  as  to  the  nature  of  solutions,  in  relation 
to  electrical  and  other  actions,  must  also  be 
applied  to  the  living  tissues.  Thus  salts  may 
act  not  as  salts,  but  in  solution  the  elements 
may  exist  separately  as  ions,  related  to  either 
the  positive  or  negative  poles  of  a  current, 
or  carrying  electrical  charges,  and  that 
physiological  activities  may  vary  according 
as  the  anion  (positive  pole  ion)  or  the  kation 
(negative  pole  ion)  comes  into  play.  There  are 
thus  in  living  matter  subtile  phenomena  of 
which  we  yet  know  very  little. 


CHAPTER  XII 

THE  REGULATING  MECHANISM.   NERVOUS 
SYSTEM 

93.  THE  nervous  system  controls  and  regulates 
all  the  organs  and  even  the  tissues  of  the  body 
while,  at  the  same  time,  all  the  organs  contri- 
bute to  its  upkeep  and  nutrition.  In  a  sense, 
too,  it  binds  together  the  various  organs  and 
systems  of  organs  so  that  they  act  harmoni- 
ously and  it  confers  individuality  on  the  body 
It  is  the  channel,  also,  by  which  influences  from 
the  external  world  act  on  the  central  nervous 
organs  through  the  organs  of  sense.  Finally 
it  is  the  seat  of  consciousness  and  of  all  mental 
operations.  The  nervous  system  is  highly 
specialized.  At  the  beginning  of  development 
it  arises  from  the  ectoderm  of  the  embryo 
and  it  pursues  its  own  mode  of  development 
So  necessary  is  it  to  the  well-being  of  the  body 

that  it  is  nourished  and  has  its  waste  products 
169 


170    PRINCIPLES  OF  PHYSIOLOGY 

removed  by  special  arrangements,  while  it  is, 
as  far  as  possible,  protected  from  injury. 

94.  Essentially,  the  nervous  mechanism 
consists  of  centres,  nerves,  and  nerve-end 
organs.  The  centres  are  in  great  masses 
constituting  the  brain  and  spinal  cord,  and 
in  smaller  masses  found  scattered  here  and 
there,  known  as  ganglia.  The  nerves  are 
found  almost  everywhere,  as  whitish  cords, 
varying  in  calibre  from  the  largest  nerves, 
such  as  the  sciatic  in  the  back  of  the  thigh, 
down  to  minute  filaments  invisible  to  the  naked 
eye  and  requiring  the  use  of  the  microscope 
for  their  detection.  Each  nerve  is  composed 
of  minute  fibres,  all  of  microscopic  dimensions, 
and  each  showing  a  central  rod  or  axis, 
surrounded  by  a  sheath,  called  the  white 
substance,  and  this,  in  turn,  usually  covered 
by  a  thin  membrane,  the  neurilemma.  These 
matters  are  all  of  soft  consistence  and  are 
apparently  structureless,  but,  by  special 
methods,  details  of  structure  may  be  seen. 
Thus  the  central  axis  is  sometimes  composed 
of  fine  fibrils,  and  the  surrounding  matter, 
the  white  substance,  is  composed  of  elongated 


THE   REGULATING  MECHANISM   171 

flattened  nucleated  cells.  The  analogy  of 
a  nerve-fibre  to  a  copper  wire  surrounded 
by  an  insulating  sheath  is  striking,  the  wire  for 
conduction  representing  the  central  rod  or 
axis,  while  the  insulating  sheath  is  the  white 
substance.  Still  it  is  only  an  analogy.  Nerve 
fibres  vary  much  in  diameter.  Many  have  no 
white  substance  ;  primitive  fibres  are  desti- 
tute of  it,  and  it  makes  its  appearance  late 
in  development.  Nerves  consisting  of  bundles 
of  fibres  divide  and  subdivide  into  more 
and  more  delicate  fibres,  until,  as  already 
pointed  out,  they  are  so  minute  as  to  be 
invisible  to  the  naked  eye.  If  we  trace  the 
axis  of  a  fibre  to  its  beginning  we  find  that  it 
always  originates  from  or  in  a  nerve  cell. 

95.  Suppose  a  nerve  were  laid  bare  and  it 
were  stimulated,  say  by  gentle  shocks  of 
electricity,  so  feeble  as  barely  to  be  felt  by  the 
tip  of  the  tongue,  one  or  more  results  might 
follow  :  (1)  a  muscle  might  contract,  and  then 
we  call  the  nerve  motor  because  it  produces 
motion  of  a  muscle  ;  (2)  a  gland  might  begin 
to  secrete,  showing  the  action  of  a  secretory 
nerve ;  (3)  blood  vessels  might  diminish  in 


172    PRINCIPLES   OF  PHYSIOLOGY 

calibre  as  occurs  when  a  vaso-motor  nerve  is 
acted  on  ;  (4)  pain  might  be  felt  when  the 
nerve  is  sensory  and  carries  impulses  to  the 
brain ;  (5)  if  it  were  a  nerve  of  special 
sense,  such  as  the  optic  or  the  auditory 
nerve,  there  would  be  a  sensation  of  light  or 
colour,  or  sound  ;  (6)  in  an  electric  fish,  the 
result  might  be  an  electric  shock  from  the 
electric  organ  These  phenomena  are  often 
complicated.  Sometimes  we  have  a  nerve 
that  has  only  one  function,  that  of  causing, 
say,  motion  or  secretion,  but  usually  a  large 
nerve  consists  of  fibres  having  different 
functions.  For  example,  a  nerve  may  contain 
both  motor  and  sensory  fibres,  and  might  serve 
in  part  to  excite  movement,  and  in  part  to 
convey  impressions  of  touch  or  temperature  or 
pain.  When  a  fibre  is  stimulated  no  physical 
change  can  be  seen  with  even  the  highest 
powers  of  the  microscope.  Nerves  may  also 
be  conveniently  classified  for  physiological 
purposes  into  (a)  centrifugal,  those  conveying 
impulses  from  nerve  centres  outwards,  and 
centripetal,  or  those  carrying  impulses  from 
the  outer  parts  of  the  body  to  nerve  centres. 


THE   REGULATING  MECHANISM   173 

96.  A  change  passes  along  a  fibre  when  stimu- 
lated. This  may  be  termed  a  nervous  impulse. 
We  do  not  know  what  this  change  is  ;  no 
movement  of  matter  can  be  observed ; 
obscure  chemical  phenomena  have  been  noted, 
as  shown  by  the  necessity  for  oxygen  and  the 
production  of  carbonic  acid.  Electrical 
charges  can  be  detected  which  seem,  like  the 
nervous  impulse,  to  pass  along  a  nerve,  but 
are  not  to  be  confounded  with  it ;  and  the 
impulse  travels  along  the  fibre  with  a  velocity 
of  only  200  feet  per  second,  incomparably 
slow,  as  compared  with  the  velocities  of 
electricity  or  sound.  Recent  observations, 
made  with  a  new  form  of  galvanometer — 
Einthoven's  string  galvanometer — a  very  sen- 
sitive instrument,  seem  to  show  that  the 
velocity  is  considerably  greater  than  has 
been  supposed.  It  would  seem  also  that  when 
the  fibre  is  stimulated  at  any  point  the 
impulse  travels  in  both  directions.  Nerve- 
fibres  are  conductors,  but,  unlike  an  electrical 
conducting  arrangement,  they  are  not  only 
conductors,  because,  at  the  point  stimulated, 
a  change  is  there  generated  which  is  then 


174    PRINCIPLES   OF  PHYSIOLOGY 

transmitted,  and  apparently  with  accumulat- 
ing energy.  So  far  as  can  be  observed,  all 
fibres  act  alike. 

97.  Nerves,  composed  of  fibres,  may  be 
divided,  and  if  rejoined  they  will  re-unite 
and  act  as  before.  This  has  led  to  the  experi- 
ment of  dividing  two  adjacent  nerves,  (a) 
motor,  and  (b)  sensory,  and  reuniting  the 
ends  so  that  the  upper  end  of  a  is  joined  to 
the  lower  end  of  b,  and  vice  versa  ;  they  may 
then  unite  and  functions  may  be  restored. 
It  is  evident  that  if  the  upper  end  of  a  was 
motor  and  conducted  downwards,  while  the 
lower  end  of  b  was  sensory  and  conducted 
upwards,  the  nervous  impulse  in  one  or  the 
other  nerve  must  now  conduct  in  the  reverse 
direction  to  what  it  did  before  division 
But  if  a  nerve  is  only  a  sensitive  conductor,  why 
are  the  results  of  stimulation  so  various  ? 
It  is  due  to  the  fact  that  the  result  depends 
on  the  apparatus  at  the  end  of  the  nerve.  If 
the  fibres  end  in  muscle,  there  will  be  motion  ; 
if  in  a  gland,  secretion  ;  if  in  a  blood  vessel, 
change  of  calibre  ;  if  in  a  special  part  of  the 
brain,  sensation  or  pain.  The  analogy  to 


THE  REGULATING  MECHANISM   175 

electrical  arrangements  is  helpful,  but  we 
must  be  careful  to  remember  it  is  only  an 
analogy.  Confusion  results  from  introducing 
words  that  have  a  definite  meaning  to  electri- 
cians, such  as  resistance.  There  is  no  evidence 
of  any  such  phenomenon  in  nerve.  If, 
however,  we  take  the  analogy  of  an  electrical 
current,  it  might  be  caused  to  produce  light, 
heat,  motion,  or  the  decomposition  of  water. 
All  would  depend  on  the  arrangements  at  the 
end  of  the  wire  conducting  the  current. 
Finally,  as  a  nerve  is  a  sensitive  conductor, 
irritation  at  any  part  of  its  course  will  always 
produce  the  same  effect.  We  may  irritate  a 
nerve  close  to  a  muscle  or  far  from  it,  but 
the  result  will  be  a  muscular  contraction. 
We  may  irritate  a  nerve  near  the  sentient 
brain,  or  far  from  it,  but  the  resultant  sen- 
sation will  be  the  same,  only,  in  this  case, 
the  origin  of  the  impulse  will  be  referred  by  the 
mind  to  the  beginnings  of  the  sensory  nerve, 
say  in  the  skin  of  the  hand.  An  illustration 
will  assist  the  reader.  Suppose  a  telegraph 
message  were  transmitted  from  Glasgow  to 
Edinburgh,  and  that  the  clerk  in  the  office  in 


176    PRINCIPLES   OF  PHYSIOLOGY 

Edinburgh  was  in  the  daily  habit  of  receiving 
such  a  message  ;  it  would  not  matter  to  him 
if  one  day  the  message  was  transmitted  to 
him  from  a  station  half  way  between  Edin- 
burgh and  Glasgow  ;  he  would  still  believe  it 
came  from  Glasgow  and  he  would,  if  necessary, 
reply  to  that  city. 

98.  It  is  convenient,  in  the  next  place,  to 
consider  the  end-organs.  These  are  highly 
specialized  organs  found  at  the  ends  of 
centrifugal  nerves,  and  at  the  beginnings  of 
centripetal  nerves.  The  endings  of  motor 
fibres  in  muscular  tissue  are  an  example  of  the 
first,  and  the  structures  in  the  skin  connected 
with  the  sense  of  touch  represent  the  second. 
End-organs  are  adapted  to  the  stimulation 
of  certain  tissues  by  the  nervous  impulse 
coming  from  a  centre  or  to  the  awakening 
of  a  nervous  impulse  by  stimuli  acting  on 
the  end-organ.  Thus  we  have  end-organs 
in  muscle  at  the  termination  of  motor 
fibres ;  nerve  fibres  can  be  traced  into 
actual  contact  with  secretory  cells  and  blood 
vessels  ;  and,  in  electrical  organs,  into  special- 
ized structures  constituting  the  electric  tissue 


THE   REGULATING  MECHANISM   177 

On  the  other  hand,  each  organ  of  a  special 
sense  has  a  terminal  organ,  such  as  the  retina 
in  the  eye,  the  various  organs  in  the  skin 
connected  with  touch,  and  the  wonderful 
arrangements  in  the  internal  ear  suitable 
for  being  acted  on  by  the  vibrations  of  sound. 
There  are  also  end-organs  in  muscle  and  in 
tendons  by  which  nervous  impulses  are 
awakened  in  these  structures  by  movements, 
and  the  impulses  so  generated  are  carried 
to  nerve  centres.  We  do  not  know  how  end- 
organs  act.  Those  of  muscle,  for  example, 
may  in  some  way  excite  the  muscle  protoplasm 
so  as  to  cause  a  kind  of  physiological  explosion 
ending  in  the  inevitable  contraction.  We  do 
not  know  how  the  nervous  impulse  acts  on 
a  secreting  cell.  Sensory  end-organs,  on  the 
other  hand,  as  we  shall  see  in  considering 
the  senses,  are  each  adapted  to  the  re- 
ception of  their  specific  kind  of  stimulus. 
Thus  the  retina  is  adapted  to  light,  the 
structures  in  the  internal  ear  to  sound,  the 
structures  in  muscle  and  tendon  to  pressure, 
and  so  on 

99.  We  have  next  to  turn  our  attention  to 

H 


178    PRINCIPLES   OF   PHYSIOLOGY 

the  central  organs,  which  are  by  far  the  most 
complicated  and  most  difficult  to  understand. 
They  consist  of  the  brain,  the  spinal  cord  or 
marrow,  and  ganglia.  Ganglia  are  small 
masses  of  nerve  matter  found  in  many  parts 
of  the  body,  and  they  abound  in  many  organs, 
as  in  the  heart  and  in  the  mesentery.  Such 
small  nodules  of  nervous  matter  consist  of 
supporting  tissue,  nerve  cells,  and  nerve  fibres. 
From  one  point  of  view,  the  spinal  marrow  and 
the  brain  may  be  regarded  as  masses  of  ganglia 
fused  together  during  countless  ages  of  evolu- 
tion. All  ganglia,  be  they  simple  or  complex, 
are  known  to  be  composed  of  certain  morpho- 
logical elements  or  structural  units.  These 
units  are  supported  and  protected  by  a 
specialized  form  of  tissue,  the  neuroglia, 
which,  however,  is  not  ordinary  connective 
tissue,  although  that  may  also  enter  into  the 
composition  of  nervous  structures.  The  units 
are  known  as  nerve-cells,  or  neurones.  These 
vary  much  in  general  form  and  size,  but 
they  have  certain  general  characteristics. 
They  are  composed  of  protoplasm  in  which 
there  is  a  well-defined  nucleus,  and  both  in 


THE   REGULATING  MECHANISM   179 

the  cytoplasm  (protoplasm  of  the  cell)  and 
in  the  nucleus,  there  are  fine  fibres  and 
networks,  while  chromatin  is  abundant  in 
the  nucleus.  In  the  protoplasm  of  the  nerve 
cell  we  find  numerous  granules.  These  are 
more  abundant  after  the  cell  has  rested  for  a 
while,  and  they  seem  to  be  used  up  during  the 
period  when  the  cell  is  active.  The  exhausted 
cell,  during  the  next  period  of  rest,  again 
becomes  crowded  with  granules  as  it  revives. 
Thus  it  behaves  like  a  secreting  cell.  Pro- 
cesses, or  as  they  have  been  called,  poles,  issue 
from  the  cell.  These  are  sometimes  few  in 
number,  but  in  many  cases  each  cell  may 
have  four,  five,  or  six  processes.  All  of  these 
processes,  except  one,  divide  and  subdivide 
so  as  to  form  smaller  and  smaller  processes, 
like  a  branch  of  a  tree  dividing  until  we 
reach  the  ultimate  twigs.  The  branch  of 
a  tree  seen  against  a  winter  sky  is  a  picture 
of  the  arrangement.  The  remaining  process 
is  the  beginning  of  the  axis  of  a  nerve  fibre, 
around  which  the  white  substance  is  developed 
at  a  later  period.  The  ultimate  unit  of  the 
nervous  system  therefore  is  now  designated 


180   PRINCIPLES   OF   PHYSIOLOGY 

as  a  neurone,  the  fine  processes  produced  by 
some  of  the  poles  constitute  branchlets  or 
dendrites ;  a  mass  of  dendrites  forms  a  dendron, 
or  tree-like  structure,  and  the  process  that  is 
the  origin  of  a  nerve-fibre  is  the  axon,  or 
central  rod.  Next,  imagine  the  branches 
of  two  adjacent  trees  freely  intermingling,  but 
not  touching  each  other.  This  is  a  picture 
of  the  relation  of  two  or  more  neurones. 
The  dendrites  do  not  form  a  network,  as  was 
once  supposed ;  they  do  not  even  touch ; 
there  is,  as  has  been  aptly  said,  contiguity 
but  not  continuity  of  structure  Where  den- 
drites come  close  together  without  touching, 
as  if  they  were  almost  clasping,  we  have 
what  is  called  a  synapsis.  The  dendrites 
may  sometimes  form  a  network  in  close 
proximity  to,  or  even  enveloping,  the  body  of, 
an  adjacent  neurone.  This  network  is  called 
an  arborization.  We  do  not  know  what 
phenomena  occur  at  a  synapse  or  arbori- 
zation. The  axon  is  a  process  of  a  neurone, 
and  it  may  be  of  great  length  or  it 
may  be  short.  Thus  axons  from  neurones 
in  the  lower  part  of  the  spinal  cord,  for 


THE   REGULATING   MECHANISM   181 

example,  may  extend  unbroken  to  the  foot. 
It  would  appear  they  may  divide  and  sub- 
divide, and  as  the  mass  of  matter  must  increase 
as  the  fibre  passes  onwards,  the  material 
forming  the  conducting  central  part  of  a 
nerve-fibre  must  also  increase.  This  has- 
been  well  established  in  the  electric  fish 
Malopterurus,  In  this  animal  the  electric 
organ  in  each  half  of  the  body  is  set  into  action 
by  the  activity  of  one  gigantic  neurone  in 
each  half  of  the  spinal  cord,  each  minute 
portion  of  the  electric  organ  is  supplied  by 
a  nerve  fibre,  and  the  sum  of  the  diameters 
of  these  fibres  is  many  thousand  times  greater 
than  the  diameter  of  the  axon  where  it  issues 
from  the  giant  neurone, 

100.  The  central  nervous  system  is  built  up 
largely  of  masses  of  neurones,  supported  by 
neuroglia.  These  masses  constitute  what  is 
called  the  grey  matter,  found  in  the  centre  of 
the  spinal  marrow  and  in  and  more  especially 
on  the  surface  of  the  brain.  Grey  matter 
is  always  supplied  by  a  very  rich  plexus  of 
capillaries  formed  by  the  subdivision  of  arteri- 
oles  ramifying  and  subdividing  in  the  mem- 


182    PRINCIPLES   OF  PHYSIOLOGY 

branes  covering  the  brain  and  cord.  A  great 
blood  supply  always  means  intense  physio- 
logical activity.  Along  with  the  grey  matter, 
in  the  central  nervous  organs,  brain  and  cord, 
there  are  strands  of  nerve  fibres  constituting 
the  white  matter.  This  is  not  so  richly  supplied 
with  blood.  In  both  brain  and  cord  there  are 
.special  arrangements  for  removing  waste 
products.  In  a  sense  the  organs  lie  in  lym- 
phatic sacs  or  bags,  and  while  there  are  no 
special  lymphatics,  each  minute  vessel  is 
surrounded  by  a  sheath,  perivascular  so-called, 
which  contains  lymph.  The  grey  matter  is 
thus  richly  nourished,  while  waste  products 
are  quickly  got  rid  of  and  carried  off. 

101.  Little  is  known  of  the  activities  of  a 
nerve-cell.  As  already  pointed  out,  granules  of 
matter  are  used  up,  but  we  do  not  know  what 
is  the  composition  of  these  granules  (Nissl's 
granules).  Chemical  substances  of  a  protein 
nature,  and  especially  rich  in  phosphorus  com- 
pounds, abound  in  the  protoplasm  of  a  nerve 
cell.  The  activity  of  the  protoplasm  depends 
more  on  an  ample  supply  of  oxygen  and  the 
removal  of  waste  matters  than  any  other  kind 


THE   REGULATING   MECHANISM    183 

of  protoplasm.  It  is  doubtful  if  the  protoplasm 
of  a  neurone,  say  in  the  brain,  can  act  for  longer 
than  a  few  seconds  without  oxygen,  and  the 
removal  of  waste  matters.  Hence  there  is 
immediate  loss  of  consciousness  if  the  supply 
of  blood  is  cut  off  from  the  cerebrum,  and  if 
the  quality  of  the  blood  be  altered  by  the 
presence  of  even  small  amounts  of  poisons 
the  effect  is  quickly  felt.  Nervous  matter  is 
also  extremely  sensitive  to  shocks  or  variations 
of  pressure.  Thus  a  sudden  concussion  will 
often  produce  unconsciousness.  The  activities 
of  the  nervous  system,  and  especially  mental 
activities,  depend  on  the  interplay  between 
grey  matter  and  blood,  and  the  limit  of 
adaptation  as  regards  blood  supply,  quality 
of  blood,  and  temperature,  is  apparently 
very  small.  Nearly  all  the  other  functions  of 
the  body,  in  a  sense,  are  working  towards 
the  end  of  the  adequate  nutrition  of  the  grey 
matter. 

102.  There  are  certain  definite  mechanisms 
connected  with  nervous  activity  that  must 
now  be  noticed.  Sometimes  if  a  sensory  nerve 
is  stimulated,  there  may  be  no  sensation  or 


184    PRINCIPLES   OF  PHYSIOLOGY 

pain,  but  movement  of  a  muscle  or  a  group  of 
muscles,  possibly  in  some  distant  part  of  the 
body.  This  is  known  as  a  reflex  action.  It 
implies  a  sensory  nerve,  by  which  an  impulse 
is  carried  to  a  centre,  a  centre  in  which  a 
change  occurs,  the  nature  of  which  we  do  not 
know,  and  a  motor  nerve  carrying  an  impulse 
to  muscles  and  causing  a  contraction.  The 
term  reflex,  although  in  general  use,  is  mislead- 
ing, as  it  suggests  something  reflected  like  a 
ray  of  light  by  a  mirror ;  but  we  have  no 
better  word  at  present.  We  know  that 
something  occurs  in  the  centre,  as  time  is 
occupied.  Assuming  the  velocity  of  the 
nervous  impulse  and  a  given  length,  both  of 
(a)  sensory  and  of  (b)  motor  nerve,  more  time 
is  occupied  in  a  reflex  action  than  the  sum  of 
times  occupied  in  a  and  b.  This  increased 
time  is  in  c,  the  centre.  Reflex  mechanisms 
play  an  important  part  in  the  body  Many 
are  very  complicated,  involving  several  sensory 
and  several  motor  nerves,  and  even  the 
centres  may  be  complicated.  As  an  example 
of  a  simplex  reflex,  we  may  take  the  move- 
ment of  winking  of  the  eyelids.  Here  the 


THE   REGULATING  MECHANISM   185 

sensory  nerve  may  either  be  the  sensory  nerve 
of  the  skin  and  of  the  eyeball  (the  fifth  cranial 
nerve),  or  the  optic  nerve  itself  through  the 
retina,  while  the  motor  nerve  is  a  branch  of 
the  seventh  cranial  nerve,  the  facial,  supplying 
the  muscle  that  closes  the  eyelids  (the  orbicu- 
laris  palpebrarum).  The  movements  of  swal- 
lowing and  the  respiratory  movements  are 
examples  of  highly  complex  reflex  actions, 
involving  many  nerves  and  many  muscles. 
We  may  or  may  not  be  conscious  of  reflex 
movements,  but  they  cannot  be  arrested  by 
an  effort  of  the  will.  Many  movements,  at 
first  consciously  performed,  become  reflex 
without  consciousness,  as  in  locomotion,  play- 
ing on  an  instrument  and  working  a  machine. 
The  centres  are  found  in  the  brain  and  cord. 
103.  The  nervous  mechanisms  we  have  con- 
sidered cause  increased  activity.  It  is  prob- 
able that  even  while  apparently  at  rest 
molecular  phenomena  are  occurring  in  nerve 
cells.  Thus  certain  nerve  fibres  issuing  from 
neurones  in  the  spinal  cord  pass  to  the  muscles- 
of  the  limbs  and  keep  these  in  a  state  of  partial 
contraction  or  tonics,  as  it  is  termed.  In  this 


186    PRINCIPLES   OF  PHYSIOLOGY 

way  muscles  are  not  loose  but  firm  and  slightly 
contracted,  even  while  at  rest.  And  when  a 
more  powerful  nervous  impulse  reaches  them, 
they  are  ready  to  contract  efficiently.  To  use 
a  nautical  phrase,  the  muscles  are  not  on  the 
"  slack  "  but  always  "  taut,"  and  no  energy 
is  lost  in  "  gathering  them  in."  But  certain 
nerve  fibres  have  the  power,  not  of  causing, 
but  of  restraining  activity.  Such  nervous 
actions  are  said  to  be  inhibitory.  A  striking 
mechanism  of  this  kind  is  seen  in  connection 
with  the  innervation  of  the  heart 

104.  This  organ  has  numerous  little  ganglia 
in  its  own  substance,  and  possibly  these  may 
have  to  do  with  its  rhythmic  contractions, 
although  this  is  doubtful.  Two  great  pairs  of 
nerves  give  off  branches  that  can  be  traced  into 
the  heart.  These  are  the  vagi,  which  come  from 
the  medulla  oblongata,  the  portion  of  the  spinal 
cord  inside  the  skull,  and  the  sympathetics, 
that  arise  from  a  chain  of  ganglia  running  along 
each  side  of  the  vertebral  column.  The  fibres  in 
these  ganglia  are  derived  from  the  cord  by  the 
anterior  roots  of  the  spinal  nerves.  Suppose  the 
heart  to  be  beating  rhythmically,  stimulation 


THE  REGULATING  MECHANISM   187 

of  the  sympathetic  in  the  neck  causes  it  to  beat 
slightly  faster,  but  stimulation  of  the  vagus, 
also  in  the  neck,  causes  the  heart  to  beat  more 
slowly ;  stronger  stimulation  may  stop  the  heart 
altogether,  and  it  will  then  be  found  that  it  is 
arrested  with  all  its  cavities  dilated,  that  is 
to  say,  the  muscle  substance  is  at  rest.  This 
action  of  the  vagus  is  said  to  be  inhibitory  or 
restraining,  while  that  of  the  sympathetic  is 
accelerating. 

105.  Such  inhibitory  phenomena  have  been 
found  in  connection  with  many  nerve  centres. 
For  example  the  sympathetic  is  the  nerve 
that  acts  on  the  muscular  walls  of  small 
vessels,  keeping  them  in  a  state  of  partial 
contraction,  and  thus,  as  already  explained, 
maintaining  a  high  blood  pressure.  If  this 
pressure  rose  too  high,  the  heart  would  have 
more  work  to  do  in  driving  the  blood  onward 
with  increased  resistance.  The  centre  (vaso- 
motor),  which  thus  acts  through  the  sympa- 
thetic, is  in  the  medulla,  and  it  is  assumed  that 
impulses  are  constantly  passing  from  it  to  the 
vessels.  This  centre,  however,  may  be  inhib- 
ited by  the  action  of  a  nerve  passing  from 


188     PRINCIPLES   OF  PHYSIOLOGY 

the  heart  upwards.  If  we  stimulate  this 
nerve,  called  the  depressor,  impulses  pass 
upwards  which  inhibit  the  centre  in  the 
medulla,  throwing  it,  as  it  were,  out  of  action, 
with  the  result  that  the  arterioles  dilate  and 
the  blood  pressure  falls.  Other  nerves  appar- 
ently may  affect  this  centre  in  an  opposite 
way,  causing  it  to  act  more  powerfully,  and 
therefore  raising  the  blood  pressure.  These 
are  called  pressor-nexves,  in  opposition  to 
the  depressors.  Most  sensory  nerves  act  as 
pressor-nerves.  Nerve  centres  are  thus  often 
under  the  action  of  impulses  having  contrary 
effects,  while  they  are  also  influenced  by  the 
quality  of  the  blood  circulating  through 
them.  Inhibitory  mechanisms  play  an  import- 
ant part  in  the  nervous  machine.  Probably 
the  restraining  powers  of  what  we  term  the 
will  have  a  physiological  basis  of  this  nature. 
106.  The  spinal  cord  may  be  regarded  as  a 
series  of  segments  combined  together  to  form 
one  mass.  Each  segment  has  a  pair  of  spinal 
nerves,  each  connected  with  the  central  grey 
matter  by  two  roots.  The  anterior  root 
consists  of  motor  fibres  carrying  nervous 


THE   REGULATING  MECHANISM   189 

impulses  outwards  from  neurones  in  the 
grey  matter.  These  fibres  mostly  supply  the 
muscles  of  the  trunk  and  limbs  on  the  same 
side.  They  also  pass  to  blood  vessels,  and 
probably  to  glands,  through  the  ganglia  of 
the  sympathetic  The  posterior  roots  con- 
sist of  fibres  that  convey  sensory  impulses 
into  the  cord.  On  this  root  there  is  a  gan- 
glion containing  neurones.  Sensory  fibres, 
coming  from  the  skin,  muscles,  and  other 
organs,  are  related  to  the  neurones  in  the 
ganglia,  and  from  these  neurones  new  fibres 
spring,  which  carry  impulses  into  the  cord. 
The  neurones  in  the  ganglia  on  the  posterior 
roots  are  the  first  receiving  stations  of 
sensory  impulses.  Many  of  such  impulses  are 
then  conveyed  upwards  to  the  brain,  and  may 
give  rise  to  sensations  of  various  kinds.  Each 
segment  of  the  cord,  however,  is  connected  with 
a  number  of  segments  both  above  and  below  it. 
Many  of  the  sensory  fibres  of  the  posterior  roots 
come  into  relation  writh  neurones  in  the  cord 
in  one  or  more  segments.  From  these  neur- 
ones axons  arise,  which  find  their  way  into 
the  anterior  roots  and  thence  to  the  muscles. 


190    PRINCIPLES   OF  PHYSIOLOGY 

Thus  we  have  many  reflex  mechanisms, 
which  do  not  involve  higher  centres.  Sensory 
fibres  pass  up  the  back  part  of  the  cord  to 
higher  and  higher  centres,  calling  forth  higher 
reflex  mechanisms,  but  many,  as  already 
indicated,  ultimately  reach  the  sensory  part 
of  the  cerebrum,  and  give  rise  to  consciousness  or 
sensations  of  various  kinds.  The  sensory  paths 
are  therefore  mainly  in  the  posterior  part  of 
the  cord,  and  these  pass  ultimately  to  the  brain 
on  the  opposite  side,  the  crossing  taking  place  in 
the  cord  and  in  the  medulla.  Thus  sensory  im- 
pulses from  the  right  side  ultimately  reach  the 
left  cerebral  hemisphere,  and  vice  versa.  Many 
sensory  impulses  also  reach  the  cerebellum,  or 
lower  brain.  Voluntary  motor  impulses  arise 
in  the  cerebrum,  pass  downwards  through  the 
lower  parts  of  the  brain,  cross  to  the  other  side 
in  the  bulb  or  medulla,  run  down  the  anterior 
part  of  the  cord,  and,  as  they  pass  down,  they 
turn  into  the  grey  matter  and  end  by  arboriza- 
tions (like  the  twigs  of  a  tree)  that  are  close  to, 
but  do  not  touch,  the  dendrites  of  large 
neurones  in  the  grey  matter.  These  give  off 
the  axons  that  become  the  nerves  of  the 


THE   REGULATING  MECHANISM   191 

muscles  Thus  these  large  neurones  in  the 
anterior  part  of  the  grey  matter  of  the  cord 
have  fibres  reaching  them  from  the  posterior 
roots,  and  are  thus  the  mechanism  of  reflex 
acts,  but  they  are  also  related  to  the  upper 
cerebral  centres  so  as  to  be  the  mechanism 
for  voluntary  acts.  It  is  important  to  notice 
that  the  axons  of  neurones  in  the  higher 
parts  of  the  nervous  system  may  become 
related  by  arborizations  to  neurones  lower 
down,  and  the  reverse  is  also  true,  lower 
neurones  becoming  similarly  related  to  higher 
ones.  It  may  only  be  an  analogy,  but  the 
whole  mechanism  suggests  a  series  of  relays 
such  as  one  might  conceive  in  a  very  extensive 
telegraphic  system.  In  a  telegraphic  relay 
the  current  may  be  caused  to  work  a  mechan- 
ism a  long  way  off ;  by  this  mechanism  another 
current  may  be  started,  and  so  on,  until  the 
terminal  station  is  reached. 

107.  It  would  appear  that  in  movements, 
such  as  those  of  locomotion,  caused  by 
antagonist  groups  of  muscles,  such  as  those 
that  bend  the  forearm  on  the  arm  (flexors) 
and  those  that  extend  the  arm  (extensors), 


192    PRINCIPLES   OF  PHYSIOLOGY 

we  have  a  kind  of  double  nervous  mechanism. 
Thus,  when  a  nervous  impulse  causes  flexors 
to  contract  there  is,  at  the  same  time,  an 
influence  which  inhibits  or  restrains  the 
extensors.  The  nervous  machinery  therefore 
is  often  very  complicated. 

108.  The  part  of  the  cerebro-spinal  system 
within  the  skull  consists  of  the  following  struc- 
tures : — (1)  a  double  chain  of  large  masses 
of  grey  and  white  nervous  matter,  forming 
from  before  backwards ;  (a)  the  corpora 
striata,  (b)  the  optic  thalami,  and  (c)  the 
corpora  quadrigemina  ;  (2)  still  farther  back 
(a)  the  pons,  (b)  the  bulb  or  medulla  ;  (3) 
covering  the  whole  of  these  masses  we  find  the 
two  hemispheres  of  the  cerebrum  ;  and  (4)  on 
the  back  of  the  pons  and  bulb  and  below  the 
posterior  part  of  the  cerebrum,  we  find  the 
cerebellum.  These  structures  are  all  connected 
with  each  other  by  strands  of  white  matter 
formed  of  nerve  fibres,  while  grey  matter  is 
found  in  masses  or  nuclei.  The  fibres 
carry  impulses  either  upwards  or  down- 
wards. There  are  also  numerous  fibres 
passing  from  one  lateral  half  of  the  brain  to 


THE   REGULATING   MECHANISM   193 

the  other  side.  The  grey  matter  in  the  pons 
and  bulb  gives  origin  to  fibres  which  run 
into  the  great  cranial  nerves,  analogous 
to,  but  much  modified  from,  the  pairs  of 
spinal  nerves.  We  may  shortly  indicate 
the  functions  of  such  nerves.  Some  of  the 
cranial  nerves  are  entirely  motor,  convey- 
ing impulses  to  the  muscles  of  the  face  on 
the  opposite  side,  such  as  the  seventh  nerve, 
that  innervates  the  muscles  of  expression  ; 
others  are  entirely  sensory,  such  as  the  optic 
and  the  auditory ;  while  a  third  class  are 
sensori-motor,  containing  both  sensory  and 
motor  fibres,  such  as  the  fifth,  the  sensory 
nerve  of  the  face,  but  which  also  contains 
motor  fibres  for  the  muscles  of  the  tongue. 

109.  The  bulb  or  medulla  contains  centres 
connected  with  respiration,  the  action  of 
the  heart,  and  the  blood  vessels.  The  latter 
is  the  vaso-motor  centre  already  referred 
to.  In  the  bulb  also  originate  the  roots  of 
some  of  the  cranial  nerves.  Passing  through 
it  we  also  find  the  motor  and  sensory 
paths  connecting  the  brain  with  the  spinal 
system  of  nerves.  It  is  important  to  notice 


194    PRINCIPLES  OF  PHYSIOLOGY 

that  both  sensory  and  motor,  especially 
motor,  tracts  cross  in  the  bulb.  This  part 
of  the  brain  is  therefore  all  important  to  life. 
If  it  is  destroyed  the  respiratory,  cardiac, 
and  vascular  mechanisms  quickly  cease.  It  is 
also  the  seat  of  reflexes  of  a  complicated 
character,  such  as  those  of  swallowing. 

110.  The  bulb  may  also  be  regarded  as 
the  most  posterior  part  of  the  brain,  or 
as  the  portion  of  the  cord  within  the 
skull.  It  is  in  a  sense  one  of  the  most 
important  centres  of  the  body  because, 
as  already  mentioned,  it  contains  centres 
for  mechanisms  absolutely  essential  to  life. 
A  study  of  its  functions  also  illustrates 
several  fundamental  principles.  Although  not 
of  large  dimensions  it  contains,  in  addition  to 
fibres  passing  through  it,  and  conveying 
impulses  upwards  and  downwards,  the  follow- 
ing centres  :  (a)  respiratory  centres  ;  (b) 
cardiac  or  heart  centres ;  (c)  vaso-motor 
centres  for  the  peripheral  blood  vessels ; 
and  (d)  centres  for  swallowing.  As  each 
centre  is  double,  owing  to  the  bilateral  sym- 
metry of  the  nervous  system,  there  are  at 


THE  REGULATING  MECHANISM   195 

least  eight  nuclei  of  grey  matter  in  the 
medulla,  all  of  which  are  important.  The 
neurones  in  this  grey  matter  are  all  intimately 
related  to  each  other.  The  bulb  is  also 
richly  supplied  with  capillary  blood  vessels, 
and  it  lies  practically  in  a  lymphatic  space 
while  perivascular  lymphatic  channels  sur- 
round its  vessels.  Waste  matters  are  thus 
quickly  removed.  All  the  blood  vessels  in 
the  bulb  are  of  remarkably  small  diameter, 
as  one  would  expect.  To  and  from  this 
centre,  or  rather  group  of  centres,  there  run 
numerous  nerve  fibres  connected  with  the 
vagi  or  pneumogastric  nerves,  and  some  of 
the  cranial  nerves.  Fibres  also  pass  into  the 
sympathetic  chain  of  ganglia. 

111.  As  already  mentioned,  the  bulb  has 
to  do  with  the  innervation  of  the  heart  and  of 
the  respiratory  mechanism.  Both  of  these 
movements  are  rhythmic  in  their  character. 
We  feel  this  in  the  beat  of  the  heart  and  in 
the  regular  periodic  movements  of  inspiration 
and  of  expiration.  If  these  movements  depend 
on  the  bulb,  the  question  arises  as  to  whether 
or  not  the  bulb  acts  automatically.  Is  there 


196    PRINCIPLES   OF  PHYSIOLOGY 

such  a  thing  as  automatic  action  in  the  nervous 
system  ?  One  can  imagine  a  nerve  centre 
acting  automatically.  Suppose  that  in  some 
way  nervous  energy  is  stored  up  in  the  centre 
until  there  is  such  a  state  of  tension  as  to 
cause  a  discharge  along  certain  nervous 
paths.  This  discharge  would  lower  the  tension 
and  there  would  be  an  interval  during  which 
energy  would  be  again  stored  until  the  next 
discharge,  and  so  on.  This  would  be  an 
automatic  mechanism.  Research  has  shown, 
however,  that  this  is  not  the  way  in  which  the 
nervous  centre  works.  It  is  not  automatic, 
but  it  is  influenced,  first,  by  the  quality  of  the 
blood  flowing  through  it,  and  it  is,  in  the 
second  place,  controlled  or  regulated  by 
nervous  impulses  coming  by  sensory  paths 
from  the  periphery.  Consider  this  with  refer- 
ence to  the  respiratory  mechanism.  In- 
spiration mainly  introduces  fresh  oxygen 
into  the  blood,  and  both  during  inspiration 
and  expiration  there  is  the  removal  of  carbonic 
acid.  When  the  blood  contains  a  certain 
proportion  of  oxygen,  even  although  carbonic 
acid  is  also  present,  it  is  bright  red  arterial 


THE  REGULATING  MECHANISM   197 

blood  ;  but  when  it  contains  more  carbonic 
acid  and  relatively  less  oxygen,  it  is  dark 
purplish-hued  venous  blood.  Again,  if  we 
breathe  deeply  a  number  of  times  in  succession 
so  as  to  introduce  as  much  oxygen  as  possible, 
we  can  then  "  hold  the  breath,"  that  is  to  say, 
we  can  for  a  time  cease  breathing.  Divers 
do  this  before  they  make  their  plunge  into  the 
sea.  In  physiological  language,  blood  con- 
taining an  excess  of  oxygen  produces  a  state 
called  apnoea,  during  which  respiration  is  sus- 
pended. On  the  other  hand,  if  the  blood 
contains  more  than  a  certain  amount  of 
carbonic  acid,  so  as  to  be  highly  venous,  there 
is  a  tendency  to  make  rapid  movements 
of  inspiration  so  as  to  get  rid  of  the  excess 
of  carbonic  acid  and  introduce  more  oxygen. 
This  happens  in  asphyxia,  produced  from  any 
cause.  These  phenomena  can  be  accounted 
for  if  we  consider  the  influence  of  the  kind  of 
blood  circulating  through  the  respiratory 
centre.  When  the  blood  is  rich  in  oxygen,  the 
centre  is  not  stimulated,  but  when  deficient  in 
oxygen  and  rich  in  carbonic  acid,  the  centre  is 
stimulated  so  as  to  produce  inspiratory 


198    PRINCIPLES  OF  PHYSIOLOGY 

movements.  Two  respiratory  centres  have 
been  by  some  assumed  to  exist  in  the  bulb — 
an  inspiratory  and  an  expiratory  centre. 
Then  carbonic  acid  may  be  supposed  to 
stimulate  the  inspiratory,  while  oxygen  might 
either  stimulate  the  expiratory  or  produce  no 
effect.  There  can  be  no  doubt,  however  we 
may  theoretically  explain  the  facts,  that  the 
quality  of  the  blood  affects  the  respiratory 
centres. 

112.  But  the  centres  for  respiration  are  also 
influenced  by  nervous  impulses  coming  from 
the  periphery.  The  lungs  are  supplied  by 
the  vagi  or  pneumogastric  nerves.  These 
contain  both  sensory  fibres  for  carrying 
nervous  impulses  upwards  to  the  bulb,  where 
the  vagi  originate,  and  motor  fibres  which 
supply  the  muscles  of  the  larynx  and  the 
muscular  fibres  in  the  walls  of  the  bronchial 
tubes.  The  larynx  is  highly  sensitive  through 
the  medium  of  a  sensory  nerve,  the  superior 
laryngeal  branch  of  the  vagus,  which  leaves 
the  main  trunk  in  the  neck  and  is  dis- 
tributed to  the  lining  membrane  of  the 
larynx.  Experiment  has  shown  that  if  the 


THE  REGULATING  MECHANISM   199 

vagus  be  divided  in  the  neck  then  irritation 
of  the  upper  end  of  the  nerve  causes  deep 
inspirations,  and  that  strong  stimulation 
may  stop  breathing  with  a  kind  of  spasm  at 
the  end  of  an  inspiration.  This  shows  that  the 
impulses  coming  from  the  lungs  are  carried 
upwards  to  the  respiratory  centre  in  the  bulb, 
and  that  they  more  especially  stimulate 
inspiration,  possibly  by  acting  on  the  in- 
spiratory  centre.  On  the  other  hand,  stimu- 
lation of  the  superior  laryngeal  branch  of  the 
vagus  causes  expirations,  and  strong  stimu- 
lation may  stop  respiration  at  the  close  of  an 
expiratory  spasm.  Impulses  therefore  coming 
sometimes  from  the  larynx  excite  expirations. 
Now  one  can  imagine  the  terminal  fibres  of 
the  vagus  in  the  lungs  to  be  stimulated  by 
venous  blood ;  impulses  would  then  be  sent 
to  the  inspiratory  centre  in  the  bulb.  This 
would  be  stimulated,  with  an  inspiration  as 
the  result.  But  inspiration  is  a  muscular  act 
involving  the  diaphragm  and  the  muscles  that 
raise  the  ribs,  while  expiration  is  an  act  mainly 
due  to  an  elastic  recoil  of  the  lungs  and  of  the 
walls  of  the  chest.  Consequently  there  is  no 


200    PRINCIPLES  OF  PHYSIOLOGY 

necessity  for  calling  into  play  the  expiratory 
centre  except  occasionally  when  there  is 
more  or  less  obstruction  to  the  free  exit  of 
air  from  the  lungs.  This  explains  the 
mechanism  of  coughing,  which  consists  of 
violent  expiratory  efforts.  But  the  inspira- 
tory  centres  may  be  influenced  through  other 
nervous  channels.  Strong  stimulation  of 
almost  any  sensory  nerves  will  cause  inspira- 
tions. Slapping  the  skin  with  a  wet  cloth, 
plunging  into  cold  water,  a  sudden  draught  of 
cold  air,  pain,  will  usually  cause  inspirations. 
Probably  the  first  breath  of  a  newly-born 
child  is  thus  excited.  Finally,  impulses  may 
come  to  the  respiratory  centres  from  the 
higher  centres  in  the  brain.  Thus,  within 
narrow  limits,  we  can  voluntarily  control  the 
breath.  When  by  certain  morbid  changes  in 
the  higher  centres,  there  is  unconsciousness, 
breathing  may  still  go  on,  but  in  a  curious, 
fitful  way,  as  if  a  mechanism  regulating  the 
respiratory  centres  had  been  interfered  with. 
So  that  the  respiratory  centres  are  maintained 
in  a  condition  of  physiological  equilibrium  by 
numerous  nervous  impulses  coming  to  them  by 


THE  REGULATING  MECHANISM   201 

sensory  filaments,  and  also  by  the  quality  of 
the  blood  flowing  through  them.  They  are 
not  automatic. 

113.  The  same  is  true  of  the  other  centres 
in  the  bulb.     Thus  the  cardiac  centres,  acting 
downwards  through  the  vagi,  tend  to  inhibit  or 
restrain  the  contractions  of  the  heart,  as  already 
explained,  while  fibres  that  find  their  way  from 
the  cord  into  the  sympathetic  have  an  accele- 
rating  action   (p.   187).     We   may   therefore 
assume  the  existence  in  the  bulb  of  inhibitory 
and  accelerating  cardiac  centres.     These  again 
are  influenced  by  peripheral  impulses.     From 
the  heart  impulses  may  pass  to  the  bulb  centres 
and  then  to  the  cerebral  centres  and  from  them 
again  downwards  to  the  centres  in  the  bulb. 
Impulses  may  also  reach  the  cardiac  centres 
along  any  sensory  nerve,  and  in  this  way  there 
may  be  a  degree  of  inhibition  or  acceleration, 
or  impulses  may  come  from  the  seat  of  con- 
scious emotion  in  the  cerebral   centres  and 
terror  may  cause  the  heart  momentarily  to 
miss  its  beats. 

114.  In  a  similar  way  the  vaso-motor  centres 
in  the  bulb  may  be  influenced.     The  action  of 


202    PRINCIPLES   OF  PHYSIOLOGY 

this  centre  is  to  maintain  the  arterioles  in  a 
certain  state  of  contraction,  and  this,  as  already 
explained,  keeps  up  the  blood  pressure.  But 
this  centre  may  be  inhibited  by  impulses 
coming  from  the  heart  by  the  depressor 
nerve  (p.  188),  while  the  centre  may  be  stimu- 
lated to  greater  activity  by  many  sensory 
nerves  which  thus  act  as  pressor  nerves  and 
raise  the  blood  pressure.  Again,  the  centre 
may  be  influenced  by  impressions  coming  to 
it  from  the  brain  centres,  thus  producing  the 
blush  of  shame  or  the  pallor  of  fear.  It  has 
been  found  that  the  vaso-motor  centre  pos- 
sesses a  kind  of  inherent  rhythm.  Thus  when 
all  peripheral  impulses  have  been  prevented  as 
far  as  possible  from  reaching  it,  the  blood 
pressure  still  goes  through  a  slow  series 
of  variations — that  is  to  say,  the  muscular 
walls  of  the  arterioles  have  a  slow  rhythmic 
movement,  contracting  and  expanding  in 
obedience  to  impulses  still  coming  from  the 
vaso-motor  centre.  (Traube-Hering  curves  of 
blood  pressure). 

115.  These  nervous  mechanisms  are  pictures 
of  the  mode  of  action  of  all  nerve  centres. 


THE  REGULATING  MECHANISM   203 

There  is  no  automatism,  at  all  events  in 
the  nervous  centres,  but  rather  a  series  of 
changes  induced  by  the  quantity  and  the 
quality  of  the  blood  and  by  nervous  impulses 
from  many  quarters  Thus  the  body  works 
as  a  whole.  There  is  no  autocratic  centre ; 
the  most  autocratic,  the  cerebrum  itself,  the 
seat  of  what  we  term  the  will,  comes  under 
the  same  law. 

116.  The  pons  consists  mainly  of  great  trans- 
verse bands  of  fibres  passing  from  one  side  of 
the  cerebellum  to  the  other.     In  it  there  are 
bundles  of  fibres  passing  upwards  and  down- 
wards and  masses  of  grey  matter  for  some 
of  the  roots  of  cranial  nerves.     The  pons  is 
intimately  related  to  the  cerebellum,  as  the 
transverse  fibres  form  what  are  known  as  the 
middle  peduncles  of  that  organ. 

117.  Immediately  above  the  pons  we  find 
the  crura  or  peduncles  of  the  brain,  containing 
the  great  motor  and  sensory  paths.     They 
also  contain  numerous  fibres  connecting  the 
cerebellum    with    the    cerebrum.     Near    the 
peduncles    we   find    four   small    bodies,    the 
corpora  quadrigemina.     These  consist  of  layers 


204    PRINCIPLES  OF  PHYSIOLOGY 

of  white  and  grey  matter,  showing  a  >char- 
acteristic  structure,  and  connected  with  the 
fibres  that  come  from  the  retinae  of  the  eyes. 
They  are  thus  the  first  recipients  of  visual 
impressions  transmitted  by  the  fibres  of  the 
optic  nerves  These  nervous  impulses  may 
call  forth  contraction  of  the  pupil,  the  round 
aperture  in  the  iris  of  the  eye,  or  they  may 
excite  more  complex  reflexes,  along  with  the 
action  of  the  other  ganglia  in  front  of  them, 
the  optic  thalami  and  corpora  striata.  These 
impulses,  however,  do  not  give  rise  to  con- 
sciousness. A  sensation  excited  by  impulses 
coming  from  the  eyes  arises  only  when  the 
impulses  are  transmitted  upwards  from  the 
corpora  quadrigemina  to  the  visual  centre  in 
the  cerebrum.  By  the  nervous  arrangements, 
also,  the  nasal  and  temporal  halves  of  the 
retinae  are  correlated  to  each  other.  Thus 
all  the  fibres  from  the  temporal  side  of  each 
retina  pass  to  the  corpus  on  the  same  side, 
while  those  from  the  two  nasal  halves  of  the 
retinae  cross  and  reach  the  corpus  on  the  other 
side.  Thus  the  right  corpus  receives  impulses 
from  the  temporal  side  of  the  right  retina  and 


THE   REGULATING  MECHANISM   205 

the  nasal  side  of  the  left,  while  the  left  corpus 
receives  fibres  from  the  left  temporal  and  the 
right  nasal  side.  This  secures  single  vision 
with  two  eyes,  if  the  image  falls  on  correspond- 
ing parts  of  the  two  retinae,  as,  for  example,  if 
it  falls  on  the  right  temporal  and  left  nasal. 
But  if  one  image  was  formed  on  both  temporal 
or  both  nasal  halves  of  the  retina,  there  would 
be  double  vision,  as  in  squinting. 

118.  The  optic  thalami  are  sensory  centres, 
receiving  impulses  from  below,  and  from  them 
impulses  pass  upwards  to  the  cerebrum,  where 
they  excite  consciousness.     They  (a)  may  act, 
however,  as  reflex  mechanisms  in  conjunction 
with  the  two  masses  immediately  in  front  of 
them,  the  corpora  striata  (b).     These  are  motor 
centres,   receiving  impulses  from  the  motor 
regions  of   the  cortex  of   the  cerebrum  (c). 
If  a  and  b  act  together,  without  the  influence 
of  c,  there  may  be  complicated  reflex  move- 
ments, such  as  occur  in  the  walking  of  the 
somnambulist,   or  the  unconscious  perform- 
ance of  complicated  movements. 

119.  The    highest    of    all    centres    is    the 
cerebrum,  consisting  of  two  hemispheres,  show- 


206    PRINCIPLES  OF  PHYSIOLOGY 

ing  complicated  convolutions.  These  convolu- 
tions constitute  an  immense  web  of  grey  matter 
showing  numerous  neurones  of  a  peculiar 
pyramidal  form,  arranged  more  or  less  in 
layers.  Numerous  fibres  pass  in  all  directions 
connecting  one  part  of  the  cerebral  mass  with 
the  other.  All  the  structural  details  indicate 
co-ordination  of  function.  Thus  the  convolu- 
tions are  connected  by  many  associational 
fibres ;  fibres  pass  from  the  anterior  to  the 
posterior  parts  of  the  cerebrum ;  and  numerous 
fibres  form  the  great  transverse  commissure, 
known  as  the  corpus  callosum,  which  connects 
one  hemisphere  with  the  other.  Other  smaller 
transverse  commissures  exist.  The  cerebrum 
receives  nervous  impulses  from  all  parts  of 
the  body.  The  sensory  tracts  in  the  cord 
send  numerous  fibres  upwards,  and  these  reach 
the  grey  matter  of  the  cerebral  convolu- 
tions, in  the  posterior  and  lateral  regions, 
forming  arborizations  or  networks  near  motor 
neurones  that  lie  in  layers  in  the  grey  matter, 
more  especially  in  certain  convolutions  on 
the  lateral  aspect  of  the  cerebrum,  From  these 
motor  neurones  fibres  (axons)  pass  downwards 


THE  REGULATING  MECHANISM   207 

through  the  corpora  striata  into  the  peduncles 
and  then  downwards  in  the  pons  and  bulb 
(where  they  cross  or  decussate) ;  they  then 
pass  down  the  anterior  part  of  the  cord, 
until  they  reach  the  segment  or  segments 
of  the  cord,  in  which  they  end  by  becom- 
ing related  to  the  great  motor  neurones 
in  the  anterior  part  of  the  grey  matter  (see 
p.  190).  Fibres  to  and  from  the  cerebrum  are 
related  to  the  deep  origins  of  the  cranial 
nerves.  Finally,  the  cerebrum  receives  numer- 
ous fibres  from  the  cerebellum.  The  physio- 
logical mechanism  of  the  cerebrum  is  still 
obscure.  Portions  of  the  grey  matter  of  the 
convolutions  are  concerned  in  the  reception 
of  sensory  impressions  that  are  translated 
into  consciousness. 

120.  Definite  districts  of  grey  matter,  more 
especially  in  the  posterior  and  lateral  portions 
of  the  cerebrum  (temporo-sphenoidal  convolu- 
tions) receive  messages  that  are  translated 
into  sensations  of  touch,  pressure,  temperature, 
vision,  and  hearing.  These  areas  constitute 
what  are  termed  centres  for  the  special  senses. 
No  centre  has  been  identified  with  taste. 


208    PRINCIPLES   OF  PHYSIOLOGY 

The  olfactory  bulbs  and  their  roots  are  con- 
nected with  smell.  In  the  middle  region,  on 
each  side  of  the  great  fissure  known  as  the 
Sylvian  fissure,  we  find  definite  motor  centres, 
connected  with  the  muscles  and  limbs  and 
with  the  muscles  of  the  tongue  and  face  on 
the  opposite  side ;  indeed  it  is  highly  probable 
that  every  muscle  of  the  body,  even  the  laryn- 
geal  muscles  associated  with  the  production 
of  voice,  has  a  centre  in  the  cerebrum. 
When  these  motor  centres  are  irritated  by 
feeble  electric  shocks,  movements  of  certain 
muscles  occur  on  the  opposite  side  of  the  body. 
Thus,  stimulation  of  one  centre,  say  on  the 
right  side  of  the  cerebrum,  will  cause  a  move- 
ment of  one  of  the  muscles  of  the  left  hind  leg. 
Again,  stimulation  of  another  centre  will 
cause  movement  of  the  left  fore  leg.  There 
are  complex  centres  for  the  lips,  tongue,  etc. 
It  must  not  be  supposed,  however,  that  these 
motor  centres  are  isolated  or  that  they  can 
originate  impulses.  No  doubt  they  are  called 
into  action  by  nervous  impulses  of  a  sensory 
character  coming  from  other  parts  of  the 
cerebrum,  or  from  below.  Thus  they  also 


THE  REGULATING  MECHANISM   209 

constitute  a  reflex  mechanism ;  this  appears 
to  be  the  general  plan  on  which  the  whole 
nervous  system  is  constructed. 

121.  This  fact  is  illustrated  by  associated 
movements,  such  as  those  of  speech  or  of  the 
hand  in  penmanship.  A  spoken  word  rouses 
the  auditory  centre  ;  this  transmits  an  impulse 
to  the  motor  centres  of  the  speech  mechanism  ; 
and  the  word  may  be  audibly  repeated.  Or 
the  message  from  the  auditory  centre  may 
reach  the  centres  for  the  ringers  and  arm  of  the 
right  hand  and  the  word  spoken  may  now  be 
written.  Again,  the  sensory  impressions  may 
come  from  the  eye  to  the  visual  centre,  and  it 
in  turn  may  excite  speech  or  the  movements  of 
the  ringers  and  hand.  These  impulses  may 
be  also  transmitted  to  parts  of  the  cerebrum 
and  give  rise  to  consciousness.  Sometimes  in 
disease  one  of  the  links  in  this  physiological 
chain  may  be  broken.  A  patient  suffering 
from  some  form  of  cerebral  disease,  when  asked 
the  question,  "  What  is  your  name  ?  "  may  be 
unable  to  answer,  not  because  he  does  not 
hear  (he  is  not  deaf),  but  because  he  cannot 
utter  the  words  "  John  Smith  "  in  response, 


210    PRINCIPLES  OF  PHYSIOLOGY 

as  the  route  of  the  message  from  the  auditory 
centre  to  the  speech  centre  has  been  inter- 
rupted. If  the  physician  writes  the  words, 
"  Is  not  your  name  John  Smith  ?  "  and  puts 
the  paper  before  the  patient's  eyes,  there  is 
the  response :  "  Yes,  certainly."  Here  the 
message  from  the  visual  centre  reaches  the 
speech  centre,  and  the  patient  can  utter  his 
name.  Frequently  also,  a  patient  in  certain 
cerebral  diseases  may  be  perfectly  conscious  of 
the  name  of  a  particular  thing  that  he  wants, 
say  a  pencil,  but  he  has  forgotten  the  word 
or  uses  a  wrong  one,  to  his  own  annoyance, 
All  this  may  be  represented  by  diagrams,  but 
we  must  never  forget  that  diagrams  only 
represent  men's  notions  and  that  the  real 
mechanism  may  be  something  very  different. 
The  functions  of  the  anterior  lobes  of  the  cere- 
bral hemispheres  are  unknown.  Some  have 
supposed  that  in  them  we  have  the  mechanism 
for  volition  and  the  impulses  that  follow  it. 

122.  The  cerebellum  is  a  regulating  mechan- 
ism. It  may  have  other  functions,  but  it 
undoubtedly  co-ordinates  movements.  By 
co-ordination  we  mean  that  the  time  and 


THE  REGULATING  MECHANISM    211 

extent  and  order  of  a  given  group  of  muscular 
contractions  must  be  regulated  to  obtain  a 
required  result.  Thus  in  writing,  many 
muscles  of  the  arm,  fore-arm,  and  fingers  act. 
Again,  in  walking,  complicated  groups  of 
muscles  must  combine.  It  seems  that  in  all 
such  mechanisms  sensory  impulses,  or  rather 
impulses  from  the  periphery,  of  which  we  may 
or  may  not  be  conscious,  start  the  mechanism. 
Thus,  in  walking,  impulses  may  come  from  the 
skin  of  the  feet  and  from  the  muscles  and 
tendons  of  the  limb  or  from  the  eyes.  If  these 
impulses  reach  the  cerebrum,  we  may  be 
conscious  of  them.  Without  these  impulses 
even  voluntary  motion  is  irregular  and  ineffi- 
cient. But  many  may  find  their  way  to 
the  back  part  of  the  cord  and  from  it  to  the 
cerebellum  by  what  are  called  the  inferior 
peduncles  of  that  body,  which  connect  it 
with  the  cord.  The  structure  of  the  grey 
matter  of  the  cerebellum  is  extremely  com- 
plicated, and  although  many  details  are  known 
to  histologists,  we  can  form  no  conception  of 
its  mechanism.  But  the  grey  matter  shows 
the  usual  plan  of  neurones  of  various  forms,  in 


212    PRINCIPLES   OF  PHYSIOLOGY 

layers.  Round  these  neurones  fibres  that  come 
from  below  form  arborizations.  From  these, 
fibres  proceed  that  find  their  way  to  the 
cerebral  hemisphere  on  the  opposite  side  and 
probably  end  in  the  motor  centres.  The 
function  of  the  cerebellum  seems  to  be  to 
arrange  these  sensory  impulses  and  to  transmit 
them  to  the  special  motor  centre  in  the  cortex 
of  the  cerebrum,  so  as  to  bring  about  the 
co-ordination  that  is  necessary  for  the  required 
movement.  Probably  they  do  this  by  setting 
into  action  motor  centres  for  the  movements 
of  special  muscles.  There  is  a  faint  analogy 
in  the  card  of  a  Jacquard  loom,  which  so 
arranges  the  threads  as  to  enable  the  other 
mechanisms  to  weave  the  desired  pattern. 
Finally,  the  cerebellum  receives  impulses 
from  the  retina  and  from  the  internal  ear, 
and  more  especially  from  the  semi-circular 
canals  of  that  organ.  Such  impressions  from 
these  sense  organs  assist  in  the  co-ordination 
of  movement,  and  in  the  maintenance  of 
equilibrium. 

123.  It  cannot  be  too  strongly  emphasized 
that    our    knowledge    of    the    physiological 


THE  REGULATING  MECHANISM   218 

mechanism  of  the  brain  is  still  very  imperfect. 
When  we  examine  under  the  microscope 
sections  that  have  been  prepared  by  modern 
methods,  we  are  bewildered  while  we  admire, 
and  there  is  often  the  involuntary  exclama- 
tion, "  How  does  it  all  work  ?  " 


CHAPTER   XIII 

RELATION    TO     THE     OUTER    AND     INNER 
WORLDS    BY    THE     SENSES 

124.  WHEN  we  reflect  on  the  physiological 
nature  of  the  senses,  we  find  that  the  mind 
becomes  cognizant  of  two  worlds  from  which 
apparently  come  streams  of  feeling.  There  is 
in  the  first  place  the  inner  world  of  our  own 
body  in  which  there  are  physiological  opera- 
tions constantly  going  on,  such  as  have  been 
indicated  in  the  previous  pages.  Of  some 
of  these  operations  we  are  more  or  less  con- 
scious, while  many  others,  and  probably  by 
far  the  greater  number,  never  rise  to  the  level 
of  consciousness  even  although  nervous  im- 
pulses from  many  organs  and  tissues  may  reach 
the  higher  centres.  But  we  have  what  may  be 
termed  internal  senses,  such  as  hunger  and 
thirst,  satiety,  the  feeling  of  easy  and  com- 
fortable respiration,  as  when  we  breathe  fresh 

214 


THE  OUTER  AND  INNER  WORLDS  215 

air,  or  have  a  feeling  of  the  enjoyment  of 
life,  such  as  one  has  in  a  state  of  health  while 
in  the  open  air  and  in  fine  weather.  As  a 
rule,  we  pay  little  attention  to  these  internal 
senses,  which  seem  to  be  on  the  very  thresh- 
hold  of  feeling,  but  we  are  more  or  less  con- 
scious of  them  when  they  rise  to  a  certain 
intensity.  Of  many  organs  we  are  uncon- 
scious, except  when  the  nervous  impulses 
coming  from  them  cause  sensations  that  rise 
to  the  level  of  pain.  No  doubt  the  nervous 
centres  are  almost  constantly  receiving  ner- 
vous impulses  which,  although  they  may  not 
rise  into  the  sphere  of  consciousness,  yet  fill 
up,  as  it  were,  the  interstices  of  our  conscious 
life  and  give  it  completeness.  There  do  not 
appear  to  be  any  special  mechanisms  for  these 
internal  senses.  The  ordinary  sensory  or 
centripetal  nerves  serve  the  purpose. 

125.  But  we  become  cognizant  of  the  outer 
world  by  the  five  external  senses  of  vision, 
hearing,  touch,  taste,  and  smell,  and  we 
learn  about  our  position  and  movements  in 
the  outer  world  by  nervous  impulses  concerned 
in  what  is  called  the  muscular  sense,  and  in  the 


216    PRINCIPLES   OF  PHYSIOLOGY 

sense  of  equilibrium,  and  of  the  position 
of  the  head  in  space.  These  external  senses 
have  always  a  special  mechanism,  namely 
(a)  an  end  organ  adapted  for  the  reception  of 
a  specific  kind  of  stimulus ;  (b)  a  nerve  of 
special  sense  ;  and  (c)  an  internal  receptive 
organ  in  the  brain,  which  may  act  without 
consciousness  in  reflexes,  or  with  conscious 
perception  in  the  cerebrum.  As  an  example 
take  the  sense  of  vision.  The  normal  stimulus 
is  light,  the  end  organ  is  the  retina,  the  nerve 
is  the  optic  nerve,  the  recipient  centre  is  in 
the  first  instance  the  corpora  quadrigemina, 
or  optic  lobes  (as  they  are  termed,  for  example, 
in  birds),  and  the  centre  of  sensations  of  light 
and  colour  are  in  the  cerebrum,  more  especially 
in  a  special  area  of  grey  matter. 

126.  The  senses  may  be  classified  thus : 
(a)  Those  in  which  the  stimulus  is  movement 
or  pressures,  namely — touch,  hearing,  the 
muscular  sense,  and  the  sense  of  equilibrium  ; 
and  (b)  those  in  which  the  stimulus  is  more 
of  a  molecular  character,  implying  chemical 
action,  namely — vision,  taste,  and  smell.  In 
the  outer  world,  according  to  the  conceptions 


THE  OUTER  AND  INNER  WORLDS  217 

of  modern  physics,  matter  is  in  a  constant 
state  of  movement,  and  we  also  assume  the 
movements  of  the  ether  as  the  cause  of  the 
phenomena  of  heat,  light,  and  electricity. 
Such  movements  impinge  on  the  body  of  an 
animal  of  the  simplest  type,  and  by  a  slow 
process  of  evolution  through  countless  ages 
sense  organs  and  a  nervous  system  have  been 
produced.  Thus  a  pigmented  spot  has  slowly 
become  an  organ  of  vision,  and  a  few  special- 
ized hairs  have  been  developed  into  a  recipient 
organ  for  variations  of  pressure,  a  rudimentary 
organ  of  touch  or  of  hearing.  As  we  ascend 
the  scale  of  animal  life,  the  sense  organs 
become  more  and  more  complicated  until  we 
find  them  as  in  man  and  in  the  higher  animals. 
Each  sense  organ,  as  already  pointed  out, 
is  adapted  to  its  specific  kind  of  stimulus. 
Thus  the  retina  is  attuned  to  receive  the 
vibrations  of  light,  and  in  the  skin  and  in  the 
internal  ear  we  have  structures  adapted  for 
receiving  variations  of  pressure.  These  end 
organs  are  composed,  putting  the  matter  in  a 
general  way,  of  (a)  modified  epithelial  cells 
to  protect  and  support ;  (b)  a  highly  special- 


218    PRINCIPLES  OF  PHYSIOLOGY 

ized  form  of  nervous  epithelium,  which,  in  its 
turn,  is  continued  into  neurones,  and  these 
neurones  ultimately,  with  probably  inter- 
mediary neurones,  end  in  neurones  in  the 
cerebrum.  This  is  well  seen  in  the  retina, 
where  the  specialized  receptive  epithelium 
forms  the  remarkable  layer  of  rods  and  cones 
(Jacob's  membrane) ;  the  rods  and  cones  and 
other  structures  of  the  retina  are  supported  by 
modified  epithelium,  forming  structures  called 
the  Mullerian  fibres  ;  the  layers  of  granules 
in  the  retina  and  the  layer  of  large  multipolar 
nerve  cells  constitute  the  neurones.  From 
these  latter  arise  the  fibres  of  the  optic  nerve, 
which,  as  already  pointed  out,  carry  impulses 
to  the  corpora  quadrigemina,  and  thence  to 
he  cerebrum. 

127.  The  nerve  of  special  sense  is  normally 
stimulated  by  the  end  organ,  but  it  may  be 
stimulated  in  other  ways,  as  by  pressure  or 
electric  shock.  Thus  pressure  on  the  eyeball 
will  give  rise  to  dazzling  impressions  of  light 
(phosgenes).  But  the  law  is  that  in  whatever 
way  the  fibres  of  the  nerve  of  special  sense  is 
stimulated,  the  sensation  is  always  of  the 


THE  OUTER  AND  INNER  WORLDS  219 

same  kind.  Thus  a  luminous  sensation  always 
follows  stimulation  of  the  optic  nerve.  When 
it  is  divided  by  the  surgeon,  in  removal  of  an 
eyeball,  if  the  patient  is  conscious,  there  is  no 
pain  but  the  consciousness  of  a  flash  of  light. 
The  same  applies  to  all  the  other  senses. 
This  law  has  been  called  the  law  of  the 
specific  energy  of  the  nerves  of  special  sense, 
but  it  does  not  imply  that  the  nerve  is  anything 
else  than  a  conductor.  The  effect  is  due,  as 
has  already  been  explained,  to  the  arrange- 
ments at  the  cerebral  end  of  the  nerve,  by 
which  the  messages  are  always  translated  into 
sensations  of  the  same  kind. 

128.  Each  sense  organ  works  within  certain 
limits.  Thus  a  stimulus  may  be  so  feeble  as 
not  to  produce  an  effect.  This,  as  regards 
intensity,  is  the  threshold  of  sensation.  The  end- 
organ  is  adapted  to  respond,  say  to  vibrations, 
within  a  certain  range.  Thus,  if  we  look  at 
a  spectrum  the  eye  does  not  recognize  light 
or  colour  below  the  lower  limit  of  the  red,  but 
we  know  that  there  are  vibrations  in  existence 
that  give  rise  to  heat  below  the  red  end.  The 
skin  may  be  affected  by  these  low  vibrations, 


220    PRINCIPLES  OF  PHYSIOLOGY 

but  not  the  retina.  As  we  pass  upwards, 
either  by  increasing  the  intensity  or,  as  in 
viewing  a  spectrum,  by  increasing  the  number 
of  vibrations,  sensation  continues,  and  it  may 
vary  in  intensity,  or  in  quality,  or  in  both. 

129.  The  relation  between  the  strength  of 
the  stimulus  applied  to  an  organ  of  sense  and 
the  intensity  of  the  sensation  has  been  investi- 
gated.    It  is  found  that  the  intensity  of  the 
sensation  increases  with  an  increase  in  the 
strength  of  the  stimulus,  but  in  a  peculiar  way. 
It  is  not  in  direct  proportion.     For  example, 
doubling  or  trebling  the  strength  of  the  stimu- 
lus does  not  double  or  treble  the  intensity  of 
the   sensation,    but   the   latter   increases   by 
smaller    and    smaller    increments    until    no 
difference  in  the  intensity  of  the  sensation 
can  be  observed.     Thus,  in  a  very  intense 
light  the  additional  light  of  a  candle  may  not 
be  perceived     Refinements  of  this  law  have 
been  studied,  but  the  general  principle  is  as 
above   stated.     It   is   evident   that   there   is 
thus  a  protective  action  against  injury  from 
excessive  stimulation. 

130.  With  regard  to  vibrations,  a  sensation 


THE  OUTER  AND  INNER  WORLDS  221 

arises  when  they  reach  a  certain  number, 
and  it  changes  as  they  increase.  This,  as 
already  pointed  out,  is  well  seen  in  a 
spectrum.  Proceeding  from  the  low  red 
upwards  we  pass  through  the  various  colours, 
red,  orange,  yellow,  green,  blue,  indigo  and 
violet.  The  range  is  an  octave,  that  is 
to  say,  the  number  of  vibrations  producing 
violet  are  about  double  the  number  required 
for  red.  With  the  sense  of  hearing,  the  first 
tone  audible  as  a  musical  tone  is  produced  by 
about  thirty-three  vibrations  per  second,  while 
the  highest  audible  tone  corresponds  to  a  little 
over  thirty  thousand  per  second.  Thus  the 
ear  has  in  most  individuals  a  range  of  about 
eleven  octaves.  Beyond  the  highest  audible 
sound,  there  are  however  many  vibrations 
which  make  no  impression  on  the  human 
ear,  just  as  there  are  numerous  vibrations 
beyond  the  upper  limit  of  the  violet  of  the 
spectrum,  known  to  physicists,  such  as  the 
Rontgen  rays.  These  have  no  effect  on  the 
human  retina,  and  yet  their  existence  has 
been  proved  by  special  methods  of  research. 
It  is  possible,  even  probable,  that  some 


222    PRINCIPLES  OF  PHYSIOLOGY 

animals  may  hear  sounds  that  are  inaudible 
to  man.  Our  knowledge,  therefore,  of  the 
external  world  is  limited  by  our  senses,  and 
there  may  be  many  phenomena  for  which 
we  have  no  powers  of  perception.  For 
example,  we  have  no  organ  for  the  perception 
of  changes  in  the  electrical  condition  of  sur- 
rounding matter,  and  were  we  supplied  with 
such  an  organ  a  new  world  would  be  opened 
up. 

131.  The  delicacy  of  the  sense  organs  is 
remarkable.  Thus  we  may  detect  a  pressure 
on  the  skin  of  -002  gram.  We  can  detect  the 
eighth  of  a  degree  centigrade  when  the 
temperature  of  the  skin  is  18°  C.  The 
shortening  of  a  muscle  may  be  detected  so 
small  as  -004  of  a  millimetre  (l-6,000th  of  an 
inch).  The  ear  can  detect  vibrations  of  sound 
caused  by  movements  of  molecules  of  the  air 
of  -0004  mm.  (the  1-600, 000th  of  an  inch,  or 
1-1  Oth  of  the  wave  length  of  green  light ; 
while  the  retina  is  even  more  sensitive  ; — the 
energy  of  the  feeblest  light  that  can  be  dis- 
tinguished at  a  certain  distance,  say  100 
yards,  is  of  the  same  order  of  magnitude  as 


THE  OUTER  AND  INNER  WORLDS  223 

that  of  the  feeblest  tone  that  can  be  heard  by 
the  ear  at  the  same  distance  ;  one  part  of  sul- 
phate of  quinine  can  be  detected  in  1,000.000 
of  water ;  the  odour  of  one  part  of  bromine, 
and  even  much  less  of  iodoform  may  be  de- 
tected in  1,000,000  of  air.  Possibly  the  senses 
of  some  animals  are  even  more  delicate. 

132.  Each  organ  of  sense  has  accessory 
apparatus  suitable  to  it.  Thus  the  eyeball  is 
a  camera  for  the  purpose  of  forming,  in  accord- 
ance with  the  laws  of  dioptrics,  an  image  on 
the  retina.  Vibrations  of  sound  are  conveyed 
to  the  internal  ear  by  a  complicated  conducting 
mechanism  of  a  drumhead,  a  chain  of  bones, 
and  reach  a  delicate  organ  in  the  cochlea, 
known  as  the  organ  of  Corti.  By  hair-like 
processes  in  the  semi- circular  canals  of  the 
inner  ear,  acted  on  by  pressures  of  fluid  in  the 
canals,  varying  according  to  the  position 
of  the  head,  we  appreciate  the  position  of 
the  head  in  space,  and  we  regulate  the  move- 
ments of  the  body  accordingly.  In  the 
tongue  and  nose  there  are  special  epithelial 
structures,  such  as  the  taste  bodies  and  the 
olfactory  epithelium  acted  on  by  odoriferous 


224    PRINCIPLES  OF  PHYSIOLOGY 

particles.  In  the  skin  there  are  plexuses  of 
fine  nerve  fibres,  running  even  among  the 
cells  of  the  epidermis,  which  receive  delicate 
pressures,  as  in  touch.  These  pressures  are 
also  detected  by  nerve  fibres  connected  with 
specialized  structures  formed  mainly  of  epider- 
mic cells,  such  as  touch  bodies,  tactile  cor- 
puscles, and  Paccinian  bodies.  No  special 
terminal  organs  for  temperature  have  been 
discovered  in  the  skin,  but  there  are  points  in 
the  skin  sensitive  to  heat,  others  to  cold,  and 
both  distinguishable  from  those  devoted  to 
pressure.  It  would  seem  there  are  also  pain 
spots.  There  appear  to  be  even  different 
systems  of  sensibility  in  the  skin.  If  a  sensory 
nerve  to  an  area  of  skin  is  divided,  sensibility 
may  return  if  the  ends  unite.  The  sensations 
that  return  first  have  been  termed  prolo- 
pathic,  and  depend  on  heat,  cold,  and  pain 
spots.  But  another  order  of  sensations  return 
later,  and  seem  to  depend  on  tactile  sensations 
and  a  finer  sense  of  sensibility  to  pain.  This 
kind  of  sensibility  has  been  called  epicritic. 
It  follows,  then,  that  when  we  bring  the 
finger  flat  against  a  surface  we  stimulate 


THE  OUTER  AND  INNER  WORLDS  225 

a  complicated  mechanism  giving  rise  to 
different  kinds  of  sensations.  In  recent  years 
it  has  been  more  and  more  clearly  shown 
that  in  all  the  terminal  organs  of  the  senses 
there  is  differentiation  to  a  degree  at  one  time 
unsuspected. 

133.  It  is  important  also  to  observe  that 
there  seems  to  be  no  correspondence  between 
the  physical  nature  of  the  stimulus  and  the 
sensation.  They  are  absolutely  unlike.  We 
have  acquired  knowledge  of  the  various  stimuli, 
say  light  or  sound,  by  observation,  experiment, 
hypothesis  and  theory,  but  there  is  no  simi- 
larity between  certain  wave  lengths  of  the 
ether  and  a  sensation  of  violet,  nor  between  the 
varying  pressure  of  a  wave  in  the  air  and  the 
sensation  of  a  musical  tone.  The  sound  of  an 
orchestra  may  be  represented  mathematically 
by  a  curve,  and  physically  by  variations  in  air 
pressures,  but  the  psychical  effect  is  quite  a 
different  thing.  We  pass  at  this  point  from 
the  region  of  the  physical  and  physiological 
(both  may  ultimately  be  the  same)  into  the 
still  more  occult  region  of  the  psychical. 


CHAPTER   XIV 

THE   VOICE 

134.  THE  human  voice  is  produced  by  the 
vibrations  of  the  margins  of  two  ligaments  in 
the  larynx  called  the  vocal  cords.  Voice 
should  be  distinguished  from  speech.  Many  of 
the  lower  animals  have  voice,  but  none  have 
the  faculty  of  speech  in  the  same  sense  as  we 
find  it  in  man.  There  may  be  speech  with- 
out voice  as  in  whispering,  while  in  singing  a 
musical  scale  we  have  voice  without  speech. 

135.  The  apparatus  for  the  production  of 
voice  consists  of  (a)  a  wind  chest,  the  thorax, 
by  means  of  which  a  blast  of  air  may  be  forced 
from  the  lungs  through  the  windpipe  or 
trachea  to  the  larynx ;  (b)  a  sound  box,  the 
larynx,  containing  the  vocal  cords  ;  and  (c) 
the  throat,  mouth,  and  nasal,  and  other  pas- 
sages that  modify  the  sound  produced  in  the 

larynx.     Voice  is  almost  invariably  produced 
226 


THE   VOICE  227 

during  expiration,  but  sounds  may  also  be 
produced  by  inspiratory  efforts.  The  larynx 
is  formed  of  cartilages  connected  by  ligaments 
and  more  or  less  capable  of  being  moved  on 
each  other  by  muscles,  the  muscles  of  the 
larynx.  The  chief  cartilages  are  the  thyroid 
or  shield  forming  the  prominence  known  as 
Adam's  apple.  Immediately  below  it  is  the 
cricoid  or  ring  cartilage,  shaped  somewhat 
like  a  signet  ring,  with  the  signet  directed  to 
the  back.  On  the  signet  there  rest  two  small 
cartilages,  the  arytenoids.  These  are  pyra- 
midal in  shape,  the  bases  of  the  two  pyramids 
resting  on  the  signet  of  the  cricoid  while  the 
apices  are  directed  upwards.  The  true  vocal 
cords  are  two  membranes  or  ligaments  stretched 
from  the  base  of  each  arytenoid  forwards  to 
the  thyroid.  They  are  formed  of  connective 
tissue  fibres,  with  which  are  intermingled 
many  fibres  of  elastic  tissue.  Running  in 
the  larynx  from  before  backwards  they  leave 
a  narrow  chink  between  their  free  edges 
called  the  glottis.  During  calm  inspiration 
the  glottis  is  widely  opened,  but  on  the 
approach  of  an  expiration  the  free  margins 


228    PRINCIPLES   OF  PHYSIOLOGY 

of  the  cords  come  closer  together  and  the 
glottis  becomes  much  narrower.  If  voice  is 
now  to  be  produced,  as  when  a  note  is  sung, 
the  margins  touch  and  the  glottis  is  entirely 
closed  for  an  instant.  The  pressure  of  the 
air  below  the  cords  is  increased  by  the  expira- 
tory effort,  and  there  is  a  puff  of  air  sent  out 
between  the  margins  of  the  cords.  This 
relieves  the  pressure  and  instantly  again  the 
glottis  is  closed  by  the  elasticity  of  the  cords. 
Again  the  pressure  rises  and  there  is  another 
puff  and  so  on,  and  the  margins  of  the  cords 
thus  move  with  each  puff ;  in  other  words,  they 
vibrate.  So  that  the  organ  of  voice  is  on  the 
principle  of  the  siren,  an  acoustical  instru- 
ment by  which  musical  tones  are  produced 
by  the  fusion  of  individual  puffs  of  air. 

136.  The  vocal  cords  can  be  tightened  or 
relaxed,  and  their  free  margins  can  be  separ- 
ated or  approximated  by  the  action  of  special 
muscles.  Thus,  in  singing  a  scale,  beginning 
with  the  low  note,  the  cords  are  gradually 
tightened  by  two  muscles,  the  crico-thyroids, 
passing  from  the  sides  of  the  signet  of  the 
cricord  upwards  and  forwards  to  the  thyroid. 


THE   VOICE  229 

These  muscles,  when  they  contract,  put  the 
vocal  cords  on  the  stretch,  and  the  stretch 
increases  as  the  pitch  of  the  note  rises.  If  we 
remember  that  the  true  vocal  cords  pass 
forward  from  the  arytenoids  to  the  thyroid,  and 
if  we  suppose  that  each  arytenoid  is  capable  of 
rotating  round  a  vertical  axis  passing  from  the 
apex  of  the  pyramid  to  its  base,  we  can  under- 
stand how  the  glottis  is  opened  and  closed.  Two 
small  muscles,  the  posterior  crico- arytenoids^ 
pass  from  the  signet  of  the  cricoid  to  the  outer 
angles  of  the  base  of  the  arytenoids,  and  when 
they  contract  they  so  rotate  the  arytenoids 
as  to  carry  outwards  the  cords  and  thus  they 
enlarge  the  aperture  of  the  glottis.  Their 
antagonists  are  a  pair  of  small  muscles,  the 
lateral  crico- arytenoids,  which  pass  backwards 
from  the  sides  of  the  cricoid  to  the  outer 
angles  of  the  arytenoids.  When  these  con- 
tract they  pull  the  angle  forwards  and  inwards, 
and  thus  approximate  the  cords.  By  these 
simple  mechanisms  the  position  and  tension  of 
the  cords  is  controlled.  The  amplitude  of 
movement  of  each  muscle  is  only  a  very 
small  fraction  of  an  inch,  and  yet  a  soprano 


280    PRINCIPLES   OF  PHYSIOLOGY 

vocalist  can  produce  a  trill  with  the  greatest 
distinctness. 

137.  When  we  listen  to  musical  tones 
emitted  by  the  human  voice  we  notice  varia- 
tions of  pitch,  loudness  or  intensity,  and 
quality.  Pitch  depends  on  the  number  of 
vibrations  executed  by  the  cords  in  a  given 
time,  or,  more  correctly,  on  the  duration  of 
each  vibration.  Thus  in  singing  a  note, 
say  the  middle  C  of  the  piano,  the  cords 
vibrate  about  256  times  per  second.  Each 
vibration  therefore  lasts  the  1-256  of  a 
second.  The  greater  the  number  of  vibra- 
tions in  a  given  time  the  higher  the  pitch. 
The  range  of  the  human  voice  is  about  three 
octaves — from  fa|;  (87  vibrations  per  second), 
to  sol  fcj  (768).  In  men  the  vocal  cords  are 
more  elongated  than  in  women  in  the  ratio  of 
3  :  2,  so  that  the  male  voice  is  of  lower  pitch. 
At  the  age  of  puberty,  the  larynx  grows  rapidly 
and  the  voice  of  the  boy  "  breaks  "  in  conse- 
quence of  the  lengthening  of  the  cords,  and  it 
generally  falls  about  an  octave  in  pitch.  The 
highest  pitch  reached  by  the  human  voice  is 
recorded  of  Lucrezia  Agujari,  who  was  heard 


THE   VOICE  281 

by  Mozart  to  sing  c  in  alt,  three  octaves  above 
middle  c  (2,048  vibrations),  while  the  lowest 
is  that  of  Gaspard  Forster,  who  gave  a  note 
nearly  three  octaves  below  the  middle  c  (42 
vibrations).  Musical  sounds  begin  with  about 
32  vibrations  per  second.  These  two  voices, 
therefore,  had  a  range  of  about  six  octaves, 
but  the  usual  range  between  the  lowest  bass 
and  the  highest  soprano  of  ordinary  voices 
is  three  octaves.  The  human  ear  passes 
in  range  from  32  to  33,768  vibrations  per  sec- 
ond, or  about  eleven  octaves,  and  it  is  inter- 
esting to  notice  that  the  range  of  the  human 
voice  occupies  about  the  middle  of  that  vast 
range.  It  is  said  that  some  have  been  able 
to  hear  tones  produced  by  40,000  vibrations 
per  second.  The  tone  of  the  32-foot  organ 
pipe  is  produced  by  about  32  vibrations  per 
second,  while  the  highest  tone  of  the  organ, 
that  of  the  piccolo  stop,  is  produced  by  about 
4,000  vibrations  per  second.  With  reference 
to  these  figures  it  is  interesting  to  compare 
the  range  of  the  human  voice. 

138.  Loudness  or  intensity  depends  on  the 
amplitude  of  the  vibrations  of  the  cords — the 


232    PRINCIPLES   OF  PHYSIOLOGY 

greater  the  amplitude,  or  extent  of  move- 
ment, the  louder  the  tone.  This  will  be 
largely  determined,  not  so  much  by  the  force 
of  the  current  of  air  from  the  lungs  as  by 
the  degree  of  elasticity  of  the  cords. 

139.  The  quality  or  timbre  of  the  voice 
depends  on  the  same  laws  as  determine  the 
quality  of  musical  instruments.  The  tone 
produced  by  the  vibrations  of  the  cords  is  a 
compound  tone  depending  on  a  fundamental 
tone  which  gives  the  pitch,  with  which  are 
combined  many  partials  or  overtones,  which, 
as  regards  the  number  of  their  vibrations,  are 
simple  multiples  of  the  frequency  of  the 
fundamental.  Thus,  if  the  fundamental  tone 
is  produced  by,  say,  100  vibrations  per 
second,  then  the  partials  are  in  the  order  of 
1,  2,  3,  etc. ;  that  is,  the  first  partial  corresponds 
to  200  vibrations  per  second,  the  second  to 
300,  and  so  on.  The  cavities  above  the  cords, 
such  as  the  space  immediately  above  the 
cords  and  below  the  so-called  false  cords,  the 
cavity  of  the  pharynx,  nasal  passages,  sinuses 
in  the  bones  of  the  face,  and  the  mouth,  all 
act  as  resonance  chambers.  These  develop, 


THE   VOICE  233 

by  resonance,  a  selection  of  the  overtones, 
and  thus  give  quality  to  the  voice.  A  very 
small  change  in  the  capacity  of  these 
chambers  will  alter  the  quality. 

140.  Speech  is  the  expression  of  ideas  by 
means  of  the  voice  or  by  the  breath  (without 
voice),  as  in  whispering.  Speech  sounds  are 
produced  by  the  articulating  mechanism. 
Certain  open  sounds,  more  or  less  modified, 
give  the  vowels,  which  are  musical  tones. 
So-called  consonants  are  produced  in  many 
ways,  but  these  cannot  be  here  discussed. 
The  simplest  view  to  take  of  them  is  that 
they  are  breaks  of,  or  interferences  with,  the 
current  of  air  which,  if  the  mouth  were  open, 
and  the  articulating  mechanism  were  at  rest, 
would  produce  vowel  tones.  Physiologically 
all  words  are  made  up  of  certain  sounds 
that  may  be  called  phones.  Each  phone  may 
have  its  own  pitch,  intensity,  and  quality  ; 
and  by  their  blending  a  word  is  produced. 
Each  phone  on  a  gramophone  record  is 
composed  of  curves  that  vary  as  to  number 
(pitch),  amplitude  (loudness)  and  form  (qual- 
ity), consequently  when  the  vibratory  needle 


234    PRINCIPLES   OF  PHYSIOLOGY 

again  runs  over  these  curves,  the  sound 
must  be  reproduced.  Nature  knows  nothing 
of  letters  and  syllables ;  words  are  either 
simple  phones  or  combinations  of  phones, 
and  each  phone  is  formed  of  vibrations.  This 
is  nature's  longhand  method  of  recording 
speech  :  written  or  printed  letters  and  sylla- 
bles are  a  species  of  shorthand  invented  by 
man. 


CHAPTER   XV 

DEATH 

141.  DURING  the  earlier  years  of  life  and  up 
to  the  period  of  adolescence,  the  body  increases 
in  size  and  weight.  The  processes  of  growth 
are  in  excess  of  those  of  waste.  After  adoles- 
cence, the  body  may  remain  for  many  years 
without  much  variation  in  bulk  and  weight ; 
but  even  before  middle  life  signs  of  decay  and 
degeneration  are  noticeable,  especially  in  cer- 
tain organs.  Grey  hairs  appear,  the  teeth  decay, 
there  may  be  a  diminution  in  the  elasticity 
of  parts  and  in  the  power  of  the  muscles,  and 
there  may  be  slow  changes  in  some  of  the 
internal  organs  that  are  still  compatible  with 
ordinary  health.  In  advanced  life  these 
changes  become  more  apparent.  Some  have 
supposed  that  such  changes  may  be  due 
to  the  action  of  poisonous  substances,  formed 

mainly  in  the  alimentary  canal,  and  even  the 
235 


236    PRINCIPLES   OF   PHYSIOLOGY 

phagocytic  action  of  the  colourless  cells  of 
the  blood  has  been  invoked,  but  there  is  no 
clear  evidence  in  support  of  these  views. 
In  old  age  there  is  a  gradual  process  of 
degeneration  more  or  less  of  all  the  tissues — 
the  nervous  tissues  suffer  least  and  last.  It  is 
not  easy  to  understand  why  there  should  be 
this  tendency  to  degeneration,  and  conceiv- 
ably, in  perfect  hygienic  circumstances,  and 
with  an  absolutely  clean  pedigree,  such  de- 
generation might  not  occur.  Early  death 
should  only  be  caused  by  accident.  In  an 
ideal  physiological  life,  death  should  come 
late  as  a  result  of  gradually  increasing  weak- 
ness without  pain  or  suffering,  and  it  should 
be  a  process  as  normal  as  going  to  sleep.  In 
most  instances,  however,  degenerative  changes 
do  not  affect  all  the  organs  alike.  Some,  such 
as  the  heart,  or  lungs,  or  kidneys,  probably 
on  account  of  an  error  in  the  mode  of  life,  or 
a  want  of  adaptability  to  the  environment, 
may  undergo  changes  that  unfit  them  for 
their  work.  This  disturbs  the  physiological 
balance  and  there  may  be  suffering  ending 
in  death.  When  this  occurs,  the  mechanism 


DEATH  237 

of  the  heart  or  of  breathing,  or  of  the  nervous 
system,  may  break  down,  and  death  of  the 
body  as  a  whole  takes  place.  The  organs, 
or  rather,  the  tissues  in  the  organs,  the  cells, 
the  living  matter,  die  more  slowly,  and  at 
last  these  too  cease  to  live  The  organic 
matter  of  the  body  then,  under  the  influence 
of  micro-organisms  in  the  air  or  the  soil, 
breaks  down  by  processes  of  putrefaction, 
and,  in  course  of  time,  it  is  decomposed 
into  simpler  and  simpler  organic  substances 
until  the  ultimate  elements  are  reached.  Thus 
organic  matter  becomes  again  inorganic. 

142.  The  causes  of  longevity  are  not  under- 
stood ;  nor,  as  already  mentioned,  is  it  evident 
why  the  degenerative  changes  above  referred 
to  should  come  on.  Each  species  of  animal, 
at  all  events  among  the  higher  animals, 
seems  to  be  so  constructed  as  to  have  a 
longevity  peculiar  to  the  species.  Attempts 
have  been  made  to  connect  this  in  some 
way  with  the  period  of  utero-gestation,  but 
little  reliance  can  be  placed  on  such  specu- 
lations. It  is  clear,  however,  that  longevity 
is  largely  a  matter  of  heredity,  if  accidents 


238    PRINCIPLES  OF  PHYSIOLOGY 

of  all  kinds  are  avoided.  The  contraction  of 
a  pneumonia  or  of  a  fever  in  early  life  may  be 
regarded  as  an  accident  which  has  cut  short 
the  normal  duration  of  life. 


CHAPTER   XVI 

PHILOSOPHICAL   QUESTIONS   AND   THE 
TREND    OF   PHYSIOLOGY 

143.  IN  the  brief  survey  we  have  given  of 
physiological  processes,  questions  of  a  philo- 
sophical nature  cannot  have  failed  to  occur 
to  the  mind.  There  is  one  always  keenly 
debated,  namely,  the  existence  of  a  vital  force 
or  energy,  as  distinguished  from  the  physical 
forces  with  which  we  are  acquainted.  It  does 
not  serve  any  practical  purpose  either  to 
deny  or  to  affirm  the  existence  of  such  a 
force.  As  a  matter  of  fact,  we  are  met  every- 
where with  phenomena  which  cannot  be 
explained  by  our  present  knowledge  of  physi- 
cal and  chemical  science.  Numerous  in- 
stances of  such  phenomena  have  been  pointed 
out,  and  it  is  surely  scientific  and  philosophical 
to  recognize  the  limits  of  our  knowledge.  With 
the  progress  of  science  we  may,  and  indeed 

239 


240    PRINCIPLES   OF  PHYSIOLOGY 

will,  get  further  into  the  molecular  arena,  and 
be  able  to  explain  some  of  those  phenomena, 
which  at  present  are  so  obscure.  We  need 
not  proclaim  what  we  do  not  know,  and  assert 
that  all  of  these  phenomena  are  in  reality 
physical,  because  this  is  simply  begging  the 
question.  There  are  phenomena,  however, 
which  we  may  feel  assured  can  never  be  so 
explained.  Those  of  a  mental  kind  can  never 
be  thus  accounted  for,  and  no  metaphysical 
subtleties,  either  from  a  materialistic  or  an 
idealistic  standpoint,  will  ever  satisfy  the 
mind.  How  are  we  to  give  a  physiological 
explanation  of  human  personality  ? 

144.  Progress  in  physiology  can  only  be 
made  by  a  resolute  investigation  of  all  the  vital, 
physical,  and  chemical  phenomena  that  occur 
in  living  matter  and  in  living  beings.  This  must 
be  done  by  the  methods  followed  by  physiolo- 
gists, with  all  the  help  they  can  receive  from 
the  rapid  accumulation  of  knowledge.  At  one 
time  anatomical,  at  other  times  histological, 
considerations  govern  the  science.  The  older 
anatomists  were  content  to  display  the  organs 
and  to  infer  their  functions.  The  cell  theory 


PHILOSOPHICAL   REFLECTIONS     241 

and  the  genesis  of  tissues  (not  a  hundred  years 
old)  at  one  time  seemed  to  be  the  key  to  an 
explanation  oi  ital  phenomena.  Then  came 
a  time,  not  so  long  ago,  when  physical  methods 
of  investigation  were  in  vogue,  and  it  was 
thought  that  many  phenomena  were  merely 
physical,  requiring  for  their  interpretation 
measurement,  weighing,  and  graphic  registra- 
tion. At  the  present  time,  considerations  of 
chemical  phenomena  are  prevalent  in  the 
minds  of  physiologists.  The  structure  of  the 
complex  proteins  and  other  bodies  is  being 
investigated  ;  syntheses  of  many  organic  sub- 
stances have  been  accomplished ;  even  elemen- 
tary protein-like  bodies  have  been  formed, 
and  the  formation  of  complicated  proteins  is 
within  sight.  Chemical  phenomena  in  the 
great  processes  of  respiration,  nutrition,  and 
digestion  are  being  thoroughly  investigated. 
The  agency  of  ferments  is  now  recognized  as 
all-important  not  only  in  digestion  but  in 
nutrition.  Osmotic  phenomena  in  living 
matter  have  received  recently  much  attention, 
and  some  of  the  visions  of  advanced  physicists 
as  to  the  constitution  of  matter  have  been 
9 


242    PRINCIPLES   OF   PHYSIOLOGY 

applied  tentatively  to  the  explanation  of 
physiological  processes.  The  result  is  remark- 
able. On  all  hands  it  is  admitted  that  the 
phenomena  in  living  matter  are  much  more 
complex  than  they  were  at  one  time  thought 
to  be,  and  everywhere  we  are  brought  face  to 
face  with  vital  conditions  which  modify  the 
physical  phenomena,  and  which,  at  present, 
refuse  to  be  explained.  One  may  be  sure  that 
a  century  hence  advanced  mathematicians, 
chemists  and  physicists  (the  physiologists  of 
their  day)  will  still  be  working  at  the  problems 
of  physiology. 


BIBLIOGRAPHY 


General  Biology. 

MoKendrick  :  Text  Book  of  Physiology,  vol.  I.,  chapters 
1,  2  and  3. 

Luciani :    Human  Physiology,  vol.  I.,  Introduction  and 
chapters  1,  2  and  3. 

Herbert  Spencer :    Principles  of  Biology,  voL  I.,  part  2, 
chapters  1-6. 

J.  Theodore  Merz,  History  of   European  Thought,  vol. 

II.,  chapters  8,  9,  10  and  11, 
Energy. 

Clerk  Maxwell :   Matter  and  Motion. 

Tait :    Recent  Advance  in  Physical  Science. 

Hermann  :  Translated  by  Gamgee  :  Human  Physiology. 

Helmholtz  :   Lectures  on  Scientific  Subjects,  No.  7. 

Grove  :   Correlation  of  Physical  Forces. 
TheCeU. 

E.  B.  Wilson  :  The  Cell  in  Development  and  Inheritance 
Heredity. 

J.  Arthur  Thomson  :  Heredity,  chapters  1  and  2. 
Development. 

Thomas  Bryoe  :    Quain's  Anatomy,  vol.  I.,  section  1. 
General  Physiology. 

Halliburton's  Handbook  of  Physiology. 
The  Nervous  System  and  Senses. 

(1)  Nerves  :  Gotch,  in  Schafer's  Handbook  of  Physiology, 
vol.  II.,  page  45L 

(2)  Nerve  cell :   Schafer,  op.  cit.,  vol.  II.,  page  592. 

(3)  Cerebral  cortex  :   Schafer,  op.  cit.,  voL  II.,  page  697. 

(4)  Sympathetic.     Langley,  in  Schafer,  ap.  cit.,  vol.  II., 
page  616. 

(5)  Spinal  cord  and  medulla  :  Sherringtoo,  in  Schafer,  op. 
cit.,  vol.  I.,  pages  783,  784. 

243 


244    PRINCIPLES   OF   PHYSIOLOGY 

The  Senses. 

McKendrick  &  Snodgrass,  The  Senses. 
Greenwood  :   Physiology  of  Special  Senses. 
McKendrick :   Text- Book,  vol.  II.,  especially  Hearing. 

Philosophical. 

Dastre  :  Life  and  Death. 

F.  Czapek  :  Chemical  Phenomena  in  Life. 


GLOSSARY 


Abiogenesis   (Greek,    a,  privative ;     bios,    life ;     genesis, 

production). — Spontaneous  generation. 
Accelerator  nerves   (Latin,   accelero,   to   hasten). — Nerves 

which,  when  stimulated,   quicken  the  rate  of  the 

heart's  action. 

Adrenals. — The  supra-renal  capsules. 
Adsorption  (Latin  ad,  to,  sorbere,  to  suck). — The  attraction 

of  gelatin,  etc.,  for  certain  substances  ;  not  solution. 
Afferent  (Latin  affere,  to  convey  to).     Conveying  towards, 
Afterbirth. — The  placenta. 
Agglutination   (Latin,   agglutinarey   to   cement   to). — The 

gathering  together  into  small  masses  of  bacteria. 
Anaesthesia  (Greek,  a,  privative;  aisthesis,  perception). — 

Loss  of  sensation. 
Anion. — An    electro-negative   body  that   passes    to  the 

positive  pole  during  passage  of  a  current. 
Anode  (Greek,  ana,  upwards  ;  odos,  a  way). — The  positive 

pole  of  a  battery. 
Argon   (Greek,   argos,  inactive),   a    recently   discovered 

element. 
Assimilation  (Latin,  assimilare,  to  make  like). — Conversion 

of  foodstuffs  into  living  matter. 
Axilla. — The  armpit. 
Axis  cylinder. — The  central  filament  in  a  nerve  fibre. 

Bacillus  (Latin,  bacillum,  a  little  rod). — Bacilli  are  micro- 
organisms. 

Bacteria    (Greek,   bacterion,  a    rod). — Unicellular    micro- 
organisms having  no  chlorophyll. 

Basement  Membrane. — A  delicate  membrane  on  mucou* 
and  serous  surfaces,  bearing  epithelium. 
245 


246    PRINCIPLES   OF  PHYSIOLOGY 

Blastoderm  (Greek,  blastano,  germinate;  derma,  skin)  — 
A  layer  of  cells  formed  by  repeated  division  of  the 
primitive  cells. 

Brownian  movement. — Rapid  motion  of  minute  micro- 
scopical particles,  first  described  by  R.  Brown, 
botanist. 

Brunner's  Glands. — Small  racemose  (grape -like)  glands 
found  in  the  duodenum. 

Calorimeter. — An  apparatus  for  measuring  the  heat  of 

combustion. 
Calorie. — Thermal  unit. 
Cartilage. — Gristle. 
Casein. — A  proteid,  forming  chief  constituent  of  cheese. 

Formed  from  caseinogen,  by  action  of  acids  or  rennin. 
Cathode,  or  Katode. — Negative  pole  of  a  battery. 
Cation,  or  Ration  (Greek,  katon,  that  which  goes  down). — 

An  electro-positive  body  that  passes  to  the  negative 

pole  during  the  passage  of  a  current. 
Centrosome. — A  minute  body  found  within  a  cell. 
Chemiotaxis  (Greek,  chemia,  chemistry ;    taxis,  order). — 

A  property  of  attraction  drawing  micro-organisms 

or  their  products  to  the  white  corpuscles  of  the  blood. 
Chondrin. — A  proteid  found  in  cartilage,  etc. 
Chromatin   (Greek,  chroma,   colour). — Colourable    matter 

found  in  the  nuclei  of  cells. 
Chyle  (Greek,  chylos,  juice). — A  milk-like  fluid  absorbed 

by  the  lacteal  vessels  in  the  villi  of  the  small  intestine. 
Chyme    (Greek,    chymos,    juice). — Semi-digested    matter 

that  passes  from  the  stomach  into  the  duodenum. 
Coagulation  (Latin,  con,  agere,  to  drive  together). — The 

formation  of  a  blood  clot. 
Colloids  (Greek,  kolla,  glue  or  jelly). — Non-crystallizable 

matter  that  does  not  pass  through  an  animal  mem- 
brane in  ordinary  circumstances. 
Corpus,  corpora. — Bodies,  such  as  corpora  quadrigemina, 

four  twin-like  bodies. 
Crystalloids. — Substances  that  in  dialysis  pass  through 

animal  membranes. 


GLOSSARY  247 

Cutis  vera. — The  true  skin. 

Cytoblastema  (Greek,  Tcutos,  a  cell ;    blastema,  growth). — 

Cell    protoplasm.     Cytoplasm,    protoplasmic    matter 

of  a  cell. 

Defensive  bodies. — Substances  in  the  blood  that  tend  to 
destroy  micro-organisms.  (Germicidal,  germ-destroy- 
ing-) 

Deglutition. — Act  of  swallowing. 

Deliquescent. — Melting  away  by  absorption  of  water. 

Derma,— The  skin. 

Dialysis  (Greek,  dialusis,  a  loosening). — Separation  of 
substances  by  means  of  an  animal  membrane. 

Diaphragm. — Midriff,  a  membrane-muscular  partition 
between  thorax  and  abdomen. 

Dissociation. — Splitting  up  of  compounds  without  chemical 
change. 

Duodenum  (Latin,  duodeni,  twelve). — The  first  portion  of 
the  small  intestine. 

Ectoderm,    Endoderm    (Greek,    ektos,    outward;     endon, 

inward). — Two  layers  of  the  early  embryo.     Ecto- 
derm is  sometimes  termed  the  epiblast,  and  the  endo- 

derm,  the  hypoblast. 
Elastic  tissue. — Yellow  fibrous  tissue,  found  in  certain 

ligaments. 
Emulsion  (Latin,  emulgere,  to  milk  out). — A  special  kind 

of  mixture  of  various  substances  (see  text). 
Endosmose  (Greek,  endon,  within ;   osmosis,  impulsion). — 

The  passing  of  a  fluid  through  an  animal  membrane 

from  a  rarer  into  a  denser  fluid. 
Enzymes. — Chemical  substances  secreted  by  living  cells 

or     by    micro-organisms    which    act    catalytically. 

Sometimes  termed  ferments. 
Epidermis  (Greek,   epi,  upon ;    derma,   the  skin). — The 

superficial  layer  of  the  skin,  covering  the  dermis,  or 

cutis  vera,  the  true  skin. 
Epiglottis  (Greek,  epi,  upon;    glottis,  glottis). — A  fibro- 

cartilage  in  front  of  the  glottis  to  protect  the  opening 

into  the  larynx. 


248    PRINCIPLES   OF  PHYSIOLOGY 

Epithelium  (Greek,  epithemi,  to  place  upon). — A  layer  or 

layers  of  cells  on  a  basement  membrane. 
Erythrodextrin  and  achroodextrin  are  dextrins  formed  from 

starch  by  the  action  of  saliva.     The  first  passes  into 

sugar. 

Excretion  (Latin,  excernere,  to  separate  from). 
Fallopian  Tubes. — Ducts  passing  from  the  ovary  to  the 

uterus, 
Fecundation  (Latin,  fecundare,  to  make  fruitful). — The 

blending  of  the  male  and  female  elements. 
Fermentation  (Latin,  fervere,  to  boil). — Changes  in  certain 

matters  caused  by  enzymes  or  micro-organisms. 
Fibrin  (Latin,  fibra,  a  fibre). — The  fibrous  element  in 

blood  clot. 
Fibrinogen  (fibrin  and,  Greek,  gennao,  to  produce). — The 

substance   in   blood  from   which   fibrin  is   formed. 

Fibrinoplastin,  a  globulin  in  blood. 
Ganglion   (Greek,   ganglion,   a   tumour). — A      nodule  of 

nervous  matter,  forming  a  nerve  centre.     In  it  are 

found  nerve-fibres,  nerve  cells,  and  supporting  tissue. 
Gelatin  (Latin,  gelu,  frost). — A  proteid  found  in  white 

fibrous  and  other  tissue. 
Glycogen  (Greek,  glucus,  sweet ;    gennao,  to  produce). — 

Animal  starch,  formed  chiefly  in  the  liver. 
Haem-,  Haema-,  Haemato. — Terms  applied  to  substances 

derived  from  blood,  such  as  Haemalin,  Haematoidin. 
Haemoglobin. — The  colouring  matter  of  the  blood. 
Haemolysins. — Substances  that  dissolve  red  blood  cells. 
Haematoblasts. — Small  bodies  in  blood,  or  blood  plates. 
Histology  (Greek,  histos,  a  web ;  logos,  an  account). — The 

structure  of  the  tissues. 

Hormones   (Greek,   hormao,   to   arouse). — Chemical   sub- 
stances formed  in  epithelium  which  excite  the  secre- 
tion of  glands. 
Hyperaesthesia  (Greek,  huper,  above ;  aisthesis,  sensation). 

— Excessive  sensibility. 
Hypertrophy  (Greek,  huper,  in  excess  ;  trophe,  nutrition). — 

Excess  of  nutrition. 


GLOSSARY  249 

Imbibition  (Latin,  imbibere,  to  drink  in). — The  passage  of 

fluid  into  dead  or  living  tissues. 
Inhibition  (Latin,  inhibeo,  to  restrain). — Arrest  of  function 

of  a  nerve  centre. 
Inosite  (Greek,  is,  inos,  muscle). — A  kind  of  sugar  found 

in  muscle. 
Ions. — The  dissociation  of  molecules   into   elements   or 

ions,  a  name  given  to  the  elements  of  a  liquid  set  free 

by   the  passage  through  it  of  an  electric  current 

(electrolysis).     Ions  set  free  at  the  anode  are  anions  ; 

those  at  the  katode,  kations. 
Irritability  (Latin,  irritare,  to  provoke). — The  property  of 

living  matter  by  which  it  is  affected  by  a  stimulus. 

Jejunum  (Latin,  jejunus,  hungry). — Upper  two-fifths  of 
small  intestine. 

Karyokinesis  (Greek,  karuon,  nucleus  ;  kineo,  to  move). — 
The  changes  that  occur  in  a  nucleus  in  connection 
with  cell  division. 

Keratin  (Greek,  keras,  horn). — A  substance  found  in  hairs, 
nails,  and  other  epidermic  tissues, 

Laevulose  (Latin,  laevus,  left). — One  of  the  substances 
formed  from  cane  sugar  by  the  enzyme  invertase.- 
The  other  substance  is  dextrose. 

Lysis  (Greek,  lusis,  solution). — Occurs  in  many  words,  such 
as  ana-lysis,  para-lysis,  etc. 

Macula  germinative. — The  germinal  spot  in  the  ovum. 

Malpighian  corpuscles. — Small  bodies  in  the  cortex  of  the 
kidney  consisting  of  a  plexus  of  capillaries,  forming 
a  ball,  which  is  surrounded  by  the  beginning  of  a 
uriniferous  tubule  (the  capsule).  Malpighian  glome- 
ruli,  in  the  spleen. 

Me*  (Greek,  middle) ;  mes-enteric  (Greek,  enteron). — 
Glands  :  small  lymphatic  glands  found  in  the  mesen- 
tery ;  the  membrane  which  connects  the  small 
intestine  with  the  posterior  wall  of  the  abdomen  (a 
reflection  of  the  peritoneum). 


250    PRINCIPLES   OF   PHYSIOLOGY 

Morphology  (Greek,  morphe,  form ;  logos,  an  account). — 
The  science  that  investigates  the  laws  of  form  and 
arrangement  of  parts  of  the  bodies  of  plants  and 
animals. 

Myosin  (Greek,  mus,  muscle). — A  globulin  found  in 
muscle. 

Myxoedema  (Greek,  muxa,  mucus ;  oedema,  a  swelling). — 
A  disease  in  which  the  thyroid  body  is  atrophied  and 
the  connective  tissues  of  the  body  are  infiltrated 
with  a  mucus-like  matter. 

Neuron. — A  nerve  cell.     See  text. 

Nuclein. — A  complicated  chemical  substance  containing 
phosphorus,  found  in  nuclei. 

Nucleus. — A  kernel,  a  body  found  in  cells. 

Oesophagus  (Greek,  oisophagos,  oio,  oiso,  to  carry  ;  phago, 
to  eat). — The  carrier  of  food,  the  gullet. 

Ontogenesis  (Greek,  onta,  things  ;  genesis,  creation). — The 
history  of  the  development  of  the  individual. 

Pepsin  (Greek,  pepio,  to  digest). — The  enzyme  of  the 
gastric  juice. 

Periosteum  (Greek,  periosteos,  around  the  bones). — The 
connective  tissue  covering  of  the  bones. 

Pharynx  (Greek,  pharungx,  the  throat). — The  musculo- 
membranous  bag  or  cavity  leading  into  the  gullet. 

Placenta.— The  afterbirth. 

Protein  (Greek,  proteno,  to  be  in  the  first  place). — A  sub- 
stance containing  carbon,  hydrogen,  oxygen,  and 
nitrogen.  Ex. :  Albumen  (white)  of  egg. 

Proteolysis. — The  decomposition  of  proteins. 

Protoplasm  (Greek,  protos,  first ;  plasma,  something 
formed  or  moulded). — See  text. 

Ptyalin  (Greek,  ptualon,  saliva). — The  enzyme  of  saliva. 

Pylorus  (Greek,  pule,  a  gate ;  ora,  care). — A  gate-keeper. 
The  passage  leading  from  the  stomach  into  the 
duodenum. 

Racemose  (Latin,  racemus,  bunch  of  grapes). — A  special 
form  of  gland  with  branching  ducts  and  acini  or 
pouches,  at  the  termination  of  the  smallest  ducts* 


GLOSSARY  251 

Rectum  (Latin,  rectus,  straight). — The  last  part  of  the 
bowel  terminating  at  the  anus. 

Rennin. — The  enzyme  found  in  the  fourth  stomach  of 
ruminants,  and  in  the  gastric  juice  of  young  mammals. 

Rods  and  cones. — Structures  in  the  external  layer  of  the 
retina. 

Rods  of  Corti. — Specialized  epithelium  in  the  scala  inter- 
media of  the  cochlea. 

Schizomycetes  (Greek,  schizo,  to  split;  mukes,  mukatos, 
a  mushroom). — Split  fungi  multiplying  by  fission. 

Secretin. — A  substance  in  the  duodenum  which,  by 
absorption  into  the  blood,  stimulates  the  pancreas  to 
secrete. 

Sero-therapy. — The  injection  of  specially  prepared  blood 
serum  in  the  treatment  of  various  diseases. 

Skatol  (Greek,  skas,  skatos,  dung). — A  substance  in  faeces 
arising  from  decomposition  of  proteids. 

Spermatoblast  (Greek,  sperma,  semen  ;  blastano,  to  germi- 
nate).— Cells  that  form  spermatozoa. 

Spermatozoa  (Greek,  sperma,  semen ;    zoon,  an  animal). 

Thymus  (Greek,  thumos,  an  onion). — A  blood  gland  of 
early  life  found  behind  the  breast  bone. 

Thyro  (Greek,  thureos,  a  shield). — Applied  to  thyroid 
cartilage  of  larynx,  and  the  thyroid  body. 

Trophoblast  (Greek,  tropheo,  to  nourish  ;  blastos,  a  germ). — 
A  portion  of  the  epiblastic  layers  of  the  embryo  that 
has  to  do  with  the  formation  of  the  placenta. 

Urea  (Greek,  uron,  uron). — A  crystalline  substance  found 
in  the  urine.  Uric  acid.  See  text. 

Vaso-motor. — Term  applied  to  nerves  that  govern  the 
smaller  arterioles. 


HISTORICAL    NOTES 


GREAT   PHYSIOLOGISTS 

1500— Achillini,   1461-1512.     Release    of  anatomy  from 

the  influence  of  Galen.     Practice  of  dissection. 
1530 — Vesalius,    1514-1564.       Anatomy    of    heart    and 

vessels. 
1540— Falloposis,     1528-1562.     Colombus,     died     1559. 

Circulation  valves. 

1550— Eustachius,  1520-1574.     Vessels,  etc.,  Anatomist. 
Servetus,     1509-1553.     Discovery     of     pulmonary 

circulation* 

1560 — Fabricius   al   aquapendente,    1537-1619.     Vessels. 
1580 — Caesalpinus,    1519-1603.     Anatomist.     Forerunner 

of  Harvey. 
1610— William   Harvey,    1578-1657.     Circulation   of   the 

blood.     De  motu  cordis  et  sanguinis,  published 

1628. 

1620 — Asselli,  about  1622.     Discovery  of  the  lacteaU. 
1640— Borelli,  1608-1679.     Animal   motion.     The  heart. 
1650 — Pecquet,  about  1621.     Discovery  of  thoracic  duct. 

Boyle,  1627-1691.     Laws  of  gases. 
1660 — Malpighi,  1628-1694.     Discovery  of  capillaries. 
1670 — Leeuwenhoek.     Microscopical  investigations. 
Hooke,  1635-1702.     Theory  of  respiration. 
Mayow,  1645-1679.     Theory  of  respiration. 
1680— Ruysch,  1638-1731.     Art  of  injecting  vessels. 
1700 — Boerhaave,    1668-1738.     General    physiology. 
1710— Stephen    Hales,     1677-1761.     Hydraulics    of    the 

circulation. 

Morgagni,  1682-1771.     Beginning  of  pathology. 
1740— Haller,  1708-1777.     Theory  of  muscular  irritability. 
252 


HISTORICAL   NOTES  253 

1760— John  Hunter,  1728-1793.     Action  of  vessels,  etc. 
Spallanzani,  1729-1799.     Digestive  process,  respira- 
tion, generation. 

Galvani,  1737-1798.     Animal  electricity. 
Hewson,  1719-1774.    Functions  of  blood  glands. 
1770— Volta,  1745-1826.     Electricity. 

Lamarck,   1744-1829.     Theory  of  development. 
1780— Gall,  1758-1828.     Dissection  of  brain. 
1790 — Humphry  Davy,  about  1799.     Gases  from  blood. 
1800 — Thomas  Young,  1773-1820.     Measurement  of  time, 

theory  of  colour,  hydraulics  of  circulation. 
Charles  Bell,  1774-1842.     Functions  of  nerves. 
1810— Majendie,  1783-1855.     Theory  of  absorption. 
1820 — Beaumont,  about  1824.     Gastric  digestion  in  man. 
Gemelin,  1788-1853.     Animal  chemistry. 
E.  H.  Weber,   1795-1878.    Circulation,  muscular 

action,  senses. 

Marshall  Hall,  1790-1857.     Reflex  actions. 
Flourens,  1794-1867.     Central  nervous  system. 
Poiseuille,  1799-1869.     Circulation. 
1830 — Johann   Muller,    1801-1855.     General   physiology. 
Great  handbook.     Foundation  of  modern  Ger- 
man school  of  physiologists. 
Schleiden,  1804-1872.     Cell  theory. 
Mattencei,    1811-1869.     Electro-physiology. 
Magnus,  about  1836.     Analysis  of  gases  of  blood. 
1840— Claude   Bernard,    1813-1878.     Vaso-motor  nerves, 

glycogenic  function,  etc. 
John  Goodsir,  1814-1867.    Secretion,  etc. 
Fechner,  1801-1887.     Psychophysical  actions. 
Darwin,  1809-1882.     "  Origin  of  Species,"  1859. 
Andrew    Buchanan,    1798-1882.     Coagulation    of 

blood. 
1850— Ludwig,  1816-1895.     Hydraulics  of  circulation. 

Hermann  Helmholtz,  1812-1894.     Muscle — rate  of 
nerve  impulse,   hearing,   vision,   application   of 
physical  methods  of  research, 
Donders,  1818-1890.    Vision. 


254   PRINCIPLES   OF   PHYSIOLOGY 

Du  Bois  Raymond,  1 8 1 8  - 1 896.    Electro-physiology. 

Lister,      1827-1912.      Blood-ooagulation,     micro- 
organisms, aseptic  methods  in  surgery. 
More  recent  physiologists,  chiefly  British,  whose 
writings  are  readily  available  : 

1.  Wooldridge,  Halliburton,  Hammarston,  Fischer   (syn- 

theses of  proteid-like  bodies). 

2.  Electro-physiology. — Hermann,    Kronecker,    Burdon- 

Sanderson,  Waller,  Gotch. 

3.  Respiration. — Edward  Smith,  Haldane. 

4.  Glands    and    Secretion. — Langley,    Starling,    Bayliss, 

Schafer  (internal  secretions). 

5.  Nerves. — Langley,  Gotch,  Sherrington. 

6.  Nerve  Centres. — Hitsig,     Fritsch,    Ferrier     Waldeyer 

(neuron  theory),  Golgi,  Ramon  y  Cajal,  Sherrington. 

7.  Heart. — Gaskell,  Einthoven ;  Pulse — Mackenzie. 


INDEX 


ABSORPTION,  101 

Achromatin,  40 

AgRlutinins,  115 

Agujari,  Lucrezia,  voice  of,  230 

Amylopsin,  98 

Animal  heat,  30  ;   animal  motion, 

32 

Antitoxins,  114 
Arborizations,  180 
Arteries,  121 

Arytenoid  cartilages,  227 
Asphyxia,  197 
Assimilation,  25 
Automatic    nervous    mechanism, 

196 

Bile,   97,    139;     pigments,    139; 

salts,  140 

Bile,  circulation  of,  141 
Bilirubin,  139 
Biliverdin,  139 
Blood,    109 ;    coagulation,    116 ; 

corpuscles,  112;    plates,  112 
Botany,  12 

Bowels,  excretion  by,  138 
Brunner'a  Glands,  99 
Bulb,  193 

Capillaries,  121,  122 
Carbo-hydrates,  82 
Catalytic  action,  73 
Cell,  38,  39 
Cerebellum,  216 
Cerebrum,  206 

Chemistry,  organic,   16 ;    physio- 
logical, 16 

Cholesterin  or  cholesterol,  141 
Chromatin,  40 
Chromosomes,  40,  42 
Chyme,  95 
Circulation,  118,  120 
Colloidal  matter,  20,  81 
Connective  tissues,  56 
Contractibilitv,  59 
Corpora  quadrigemina,  204 
Corpora  stricta,  205 
Creatin,  134 
Creatinin,  134 
Cricoid  cartilage,  227 
Crura  of  cerebrum,  203 
Cytoplasm,  39 

Death,  28,  235 

Decomposition,   chemical,   67 
Deglutition,  93 

Dendrons,  180  ;    dendrites,  ISO 
Development,  37 
Diaphragm,  47 


Digestion,  92 
Dissociation,  69 
Ductless  glands,  150 

Ear,  range  of,  231 

Ectoderm,  46,  47 

Electrical  fishes,  167 

Embryology,  15 

Endoderm,  4ft,  47 

End-organs,  176,  216 

Energy,  liberation  of,  161 ;  amount 

of,  166 

Enterokinase,  76 

Enzymes,  70  ;   classification  of,  75 
Epicritic,  224 
Erepsin,  76,  99 
Erythrocytes.  112 
Evolution,  20 
Excretion,  126 

Fats,  73 

Fecundation,  44 

Fibrin,  116 

Fibrinogen,  116 

Food,  92 

Forster,  Gaspard,  voice  of,  231 

Ganglia,  178 
Gastric  juice,  94 
Glycogen,  147 
Glycogenic  function,  144 
Great  intestine,  99 
Growth,  50 

Haematoidin,  140 
Haemolysins,  113 
Heart,  nerves  of,  187 
Heat,  animal,  162 
Hepatic  vein,  103 
Heredity,  45,  52 
Hippuric  acid,  136 
Hormones,  76 
Hyaloplasm,  40 

Immunity,  114 
Inhibition,  187 
Internal  secretions,  150 
Intestine,  digestion  in,  96 
Ions,  168 

Karyokinesis,  45 
Kidneys,  130 

Lacteals,  102 

Leucocytes,  59 

Lieberkutin's  glands,  99 

Lipase,  76,  98 

Living  organisms,  general  charac- 
ters of,  20,  21,  25,  26  ;  chemical 
composition  of,  21 


200 


256 


INDEX 


Lungs,  126 
Lymphatics,  110 

Malpighian  bodies,  131 
Matter  and  energy,  65,  77 
Medulla  oblongata,  194 
Mesenchyme,  48 
Mesenteric  glands,  101 
Mesoderm,  46,  48 
Motor  centres,  208 
Motor  tracts,  190,  206 
MUllerian  ducts.  48 
Muscle,  58 

Nerve  cells,  granules  in,  182 

Nerve  fibres,  170 

Nerves,     as     conductors,     175; 

effects  of  stimulating,  172 
Nervous  activities,  35 
Nervous  impulse,  rate  of,  173 
Nervous  system,  169 
Neurones,  178 
Nucleus,  39 

Nutrition,  complemental,  155 
Opsonins,  115 
Optic  thalami,  205 
Organ,  highest  tone  of,  231 
Ovary,  42 
Ovum,  42 
Oxidases,  136 
Oxidation,  66 

Pancreatic  juice,  98 

Pepsin,  76,  94 

Peptones,  95 

Phagocytes,  113 

Philosophical  questions,  239 

Phones,  233 

Phosgenes,  218 

Physics,  relations  to  physiology, 

Physiology,  comparative,  13:  de- 
finition of,  9 

Physiological  chemistry,  16 

Pituitary  body,  152 

Placenta,  50 

Plant  life,  85 

Pons  varolii,  203 

Portal  system,  102 ;    p.  vein,  102 

Proteins,  82,  105 

Protopathic,  224 

Protoplasm,  38;  building  up  of, 
156 

Proteolytic,  76 

Proximate  principles,  22,  80 

Ptyalin,  93 


Pulmonary  ventilation,  130 
Pulse,  120 
Purine  basis,  135 

Receptaculum  chyli,  101 

Reduction,  61 

Reflex  acts,  184 

Rennin,  76 

Respiration.  126 ;   nerves  of,  198 

Retina,  218 

Salts,  84 

Sciences,  relation  to  Physiology 

12,  141 
Secretion,  33 
Senses,  214;    classification,  216  • 

delicacy  of,  222 

Sensory,  centres,  207  ;    tracts,  203 
Skin,  137  ;   sensitiveness  of,  224 
Soap,  25,  99 
Somatopleure,  46,  47 
Speech,  233 
Spermatozoon,  42 
Spinal  cord,  188 
Splanchnopleure,  46,  48 
Spleen,  152 
Steapsin,  76 

Stomach,  digestion  in,  94 
Suprarenal  bodies,  151 
Synapsis,  180 
Synthesis,  69 

Thoracic  duct,  101 

Thrombin,  76, 117 

Thyroid,  150;    cartilage,  227 

Thymus,  154 

Tissues,  38,  41,  51,  55,  63 

Tonus  of  muscle.  186 

Toxins,  114 

Trophoblast,  46 

Trypsin,  76 

Urea,  16,  133 
Uric  acid,  134 
Urine,  132 

Variability,  29 
Vaso-motor  centres,  201 
Vibrations,  130 
Vocal  cords,  227 

Voice,    226 ;     mechanism,    228  : 
range  of,  230  ;   quality  of,  232 

Waste  matters  output,  125 
Wolfflan  ducts,  48 

Zoology,  12 
Zymogen,  72 


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